[PATCH stable] memcg: add refcnt for pcpu stock to avoid UAF problem in drain_all_stock()
commit 1a3e1f40962c445b997151a542314f3c6097f8c3 upstream.
There was a kernel panic happened on an in-house environment running 3.10, and the same problem was reproduced on 4.19:
general protection fault: 0000 [#1] SMP PTI CPU: 1 PID: 2085 Comm: bash Kdump: loaded Tainted: G L 4.19.90+ #7 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.15.0-0-g2dd4b9b3f840-prebuilt.qemu.org 04/01/2014 RIP: 0010 drain_all_stock+0xad/0x140 Code: 00 00 4d 85 ff 74 2c 45 85 c9 74 27 4d 39 fc 74 42 41 80 bc 24 28 04 00 00 00 74 17 49 8b 04 24 49 8b 17 48 8b 88 90 02 00 00 <48> 39 8a 90 02 00 00 74 02 eb 86 48 63 88 3c 01 00 00 39 8a 3c 01 RSP: 0018:ffffa7efc5813d70 EFLAGS: 00010202 RAX: ffff8cb185548800 RBX: ffff8cb89f420160 RCX: ffff8cb1867b6000 RDX: babababababababa RSI: 0000000000000001 RDI: 0000000000231876 RBP: 0000000000000000 R08: 0000000000000415 R09: 0000000000000002 R10: 0000000000000000 R11: 0000000000000001 R12: ffff8cb186f89040 R13: 0000000000020160 R14: 0000000000000001 R15: ffff8cb186b27040 FS: 00007f4a308d3740(0000) GS:ffff8cb89f440000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007ffe4d634a68 CR3: 000000010b022000 CR4: 00000000000006e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: mem_cgroup_force_empty_write+0x31/0xb0 cgroup_file_write+0x60/0x140 ? __check_object_size+0x136/0x147 kernfs_fop_write+0x10e/0x190 __vfs_write+0x37/0x1b0 ? selinux_file_permission+0xe8/0x130 ? security_file_permission+0x2e/0xb0 vfs_write+0xb6/0x1a0 ksys_write+0x57/0xd0 do_syscall_64+0x63/0x250 ? async_page_fault+0x8/0x30 entry_SYSCALL_64_after_hwframe+0x5c/0xc1 Modules linked in: ...
It is found that in case of stock->nr_pages == 0, the memcg on stock->cached could be freed due to its refcnt decreased to 0, which made stock->cached become a dangling pointer. It could cause a UAF problem in drain_all_stock() in the following concurrent scenario. Note that drain_all_stock() doesn't disable irq but only preemption.
CPU1 CPU2 ============================================================================== stock->cached = memcgA (freed) drain_all_stock(memcgB) rcu_read_lock() memcg = CPU1's stock->cached (memcgA) (interrupted) refill_stock(memcgC) drain_stock(memcgA) stock->cached = memcgC stock->nr_pages += xxx (> 0) stock->nr_pages > 0 mem_cgroup_is_descendant(memcgA, memcgB) [UAF] rcu_read_unlock()
This problem is, unintenionally, fixed at 5.9, where commit 1a3e1f40962c ("mm: memcontrol: decouple reference counting from page accounting") adds memcg refcnt for stock. Therefore affected LTS versions include 4.19 and 5.4.
For 4.19, memcg's css offline process doesn't call drain_all_stock(). so it's easier for the released memcg to be left on the stock. For 5.4, although mem_cgroup_css_offline() does call drain_all_stock(), but the flushing could be skipped when stock->nr_pages happens to be 0, and besides the async draining could be delayed and take place after the UAF problem has happened.
Fix this problem by adding (and decreasing) memcg's refcnt when memcg is put onto (and removed from) stock, just like how commit 1a3e1f40962c ("mm: memcontrol: decouple reference counting from page accounting") does. After all, "being on the stock" is a kind of reference with regards to memcg. As such, it's guaranteed that a css on stock would not be freed.
Cc: stable@vger.kernel.org # 4.19 5.4 Fixes: cdec2e4265df ("memcg: coalesce charging via percpu storage") Signed-off-by: GONG, Ruiqi gongruiqi1@huawei.com --- mm/memcontrol.c | 6 ++++++ 1 file changed, 6 insertions(+)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 5a366cf79821..8c04296df1c7 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2015,6 +2015,9 @@ static void drain_stock(struct memcg_stock_pcp *stock) { struct mem_cgroup *old = stock->cached;
+ if (!old) + return; + if (stock->nr_pages) { page_counter_uncharge(&old->memory, stock->nr_pages); if (do_memsw_account()) @@ -2022,6 +2025,8 @@ static void drain_stock(struct memcg_stock_pcp *stock) css_put_many(&old->css, stock->nr_pages); stock->nr_pages = 0; } + + css_put(&old->css); stock->cached = NULL; }
@@ -2057,6 +2062,7 @@ static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages) stock = this_cpu_ptr(&memcg_stock); if (stock->cached != memcg) { /* reset if necessary */ drain_stock(stock); + css_get(&memcg->css); stock->cached = memcg; } stock->nr_pages += nr_pages;
On Wed 21-02-24 16:18:01, GONG, Ruiqi wrote:
commit 1a3e1f40962c445b997151a542314f3c6097f8c3 upstream.
I think it would be good to mention that this is only a partial backport and also explain why to do a partial rather than the full one.
There was a kernel panic happened on an in-house environment running 3.10, and the same problem was reproduced on 4.19:
general protection fault: 0000 [#1] SMP PTI CPU: 1 PID: 2085 Comm: bash Kdump: loaded Tainted: G L 4.19.90+ #7 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.15.0-0-g2dd4b9b3f840-prebuilt.qemu.org 04/01/2014 RIP: 0010 drain_all_stock+0xad/0x140 Code: 00 00 4d 85 ff 74 2c 45 85 c9 74 27 4d 39 fc 74 42 41 80 bc 24 28 04 00 00 00 74 17 49 8b 04 24 49 8b 17 48 8b 88 90 02 00 00 <48> 39 8a 90 02 00 00 74 02 eb 86 48 63 88 3c 01 00 00 39 8a 3c 01 RSP: 0018:ffffa7efc5813d70 EFLAGS: 00010202 RAX: ffff8cb185548800 RBX: ffff8cb89f420160 RCX: ffff8cb1867b6000 RDX: babababababababa RSI: 0000000000000001 RDI: 0000000000231876 RBP: 0000000000000000 R08: 0000000000000415 R09: 0000000000000002 R10: 0000000000000000 R11: 0000000000000001 R12: ffff8cb186f89040 R13: 0000000000020160 R14: 0000000000000001 R15: ffff8cb186b27040 FS: 00007f4a308d3740(0000) GS:ffff8cb89f440000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007ffe4d634a68 CR3: 000000010b022000 CR4: 00000000000006e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: mem_cgroup_force_empty_write+0x31/0xb0 cgroup_file_write+0x60/0x140 ? __check_object_size+0x136/0x147 kernfs_fop_write+0x10e/0x190 __vfs_write+0x37/0x1b0 ? selinux_file_permission+0xe8/0x130 ? security_file_permission+0x2e/0xb0 vfs_write+0xb6/0x1a0 ksys_write+0x57/0xd0 do_syscall_64+0x63/0x250 ? async_page_fault+0x8/0x30 entry_SYSCALL_64_after_hwframe+0x5c/0xc1 Modules linked in: ...
It is found that in case of stock->nr_pages == 0, the memcg on stock->cached could be freed due to its refcnt decreased to 0, which made stock->cached become a dangling pointer. It could cause a UAF problem in drain_all_stock() in the following concurrent scenario. Note that drain_all_stock() doesn't disable irq but only preemption.
CPU1 CPU2
stock->cached = memcgA (freed) drain_all_stock(memcgB) rcu_read_lock() memcg = CPU1's stock->cached (memcgA) (interrupted) refill_stock(memcgC) drain_stock(memcgA) stock->cached = memcgC stock->nr_pages += xxx (> 0) stock->nr_pages > 0 mem_cgroup_is_descendant(memcgA, memcgB) [UAF] rcu_read_unlock()
This problem is, unintenionally, fixed at 5.9, where commit 1a3e1f40962c ("mm: memcontrol: decouple reference counting from page accounting") adds memcg refcnt for stock. Therefore affected LTS versions include 4.19 and 5.4.
For 4.19, memcg's css offline process doesn't call drain_all_stock(). so it's easier for the released memcg to be left on the stock. For 5.4, although mem_cgroup_css_offline() does call drain_all_stock(), but the flushing could be skipped when stock->nr_pages happens to be 0, and besides the async draining could be delayed and take place after the UAF problem has happened.
Fix this problem by adding (and decreasing) memcg's refcnt when memcg is put onto (and removed from) stock, just like how commit 1a3e1f40962c ("mm: memcontrol: decouple reference counting from page accounting") does. After all, "being on the stock" is a kind of reference with regards to memcg. As such, it's guaranteed that a css on stock would not be freed.
What does prevent from the following?
refill_stock(memcgC) drain_all_stock(memcgB) drain_stock(memcgA) rcu_read_lock() css_put(old->css) memcgA = stock->cached mem_cgroup_is_descendant(memcgA, memcgB) UAF stock->cached = NULL
Cc: stable@vger.kernel.org # 4.19 5.4 Fixes: cdec2e4265df ("memcg: coalesce charging via percpu storage") Signed-off-by: GONG, Ruiqi gongruiqi1@huawei.com
mm/memcontrol.c | 6 ++++++ 1 file changed, 6 insertions(+)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 5a366cf79821..8c04296df1c7 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2015,6 +2015,9 @@ static void drain_stock(struct memcg_stock_pcp *stock) { struct mem_cgroup *old = stock->cached;
- if (!old)
return;- if (stock->nr_pages) { page_counter_uncharge(&old->memory, stock->nr_pages); if (do_memsw_account())
@@ -2022,6 +2025,8 @@ static void drain_stock(struct memcg_stock_pcp *stock) css_put_many(&old->css, stock->nr_pages); stock->nr_pages = 0; }
- css_put(&old->css); stock->cached = NULL;
} @@ -2057,6 +2062,7 @@ static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages) stock = this_cpu_ptr(&memcg_stock); if (stock->cached != memcg) { /* reset if necessary */ drain_stock(stock);
css_get(&memcg->css);-- 2.25.1
On 2024/02/21 16:38, Michal Hocko wrote:
On Wed 21-02-24 16:18:01, GONG, Ruiqi wrote:
commit 1a3e1f40962c445b997151a542314f3c6097f8c3 upstream.
I think it would be good to mention that this is only a partial backport and also explain why to do a partial rather than the full one.
Okay. I think to fix this problem we should add refcnt relation between memcg and stock, and since higher versions have achieved this, maybe it's better to use the same code and align with them. So I put a "commit xxx upstream" here, as requested in kernel docs[1]. So yes it's a partial backport as we only need the stock part.
[1]: https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html#stab...
There was a kernel panic happened on an in-house environment running 3.10, and the same problem was reproduced on 4.19:
general protection fault: 0000 [#1] SMP PTI CPU: 1 PID: 2085 Comm: bash Kdump: loaded Tainted: G L 4.19.90+ #7 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.15.0-0-g2dd4b9b3f840-prebuilt.qemu.org 04/01/2014 RIP: 0010 drain_all_stock+0xad/0x140 Code: 00 00 4d 85 ff 74 2c 45 85 c9 74 27 4d 39 fc 74 42 41 80 bc 24 28 04 00 00 00 74 17 49 8b 04 24 49 8b 17 48 8b 88 90 02 00 00 <48> 39 8a 90 02 00 00 74 02 eb 86 48 63 88 3c 01 00 00 39 8a 3c 01 RSP: 0018:ffffa7efc5813d70 EFLAGS: 00010202 RAX: ffff8cb185548800 RBX: ffff8cb89f420160 RCX: ffff8cb1867b6000 RDX: babababababababa RSI: 0000000000000001 RDI: 0000000000231876 RBP: 0000000000000000 R08: 0000000000000415 R09: 0000000000000002 R10: 0000000000000000 R11: 0000000000000001 R12: ffff8cb186f89040 R13: 0000000000020160 R14: 0000000000000001 R15: ffff8cb186b27040 FS: 00007f4a308d3740(0000) GS:ffff8cb89f440000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007ffe4d634a68 CR3: 000000010b022000 CR4: 00000000000006e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: mem_cgroup_force_empty_write+0x31/0xb0 cgroup_file_write+0x60/0x140 ? __check_object_size+0x136/0x147 kernfs_fop_write+0x10e/0x190 __vfs_write+0x37/0x1b0 ? selinux_file_permission+0xe8/0x130 ? security_file_permission+0x2e/0xb0 vfs_write+0xb6/0x1a0 ksys_write+0x57/0xd0 do_syscall_64+0x63/0x250 ? async_page_fault+0x8/0x30 entry_SYSCALL_64_after_hwframe+0x5c/0xc1 Modules linked in: ...
It is found that in case of stock->nr_pages == 0, the memcg on stock->cached could be freed due to its refcnt decreased to 0, which made stock->cached become a dangling pointer. It could cause a UAF problem in drain_all_stock() in the following concurrent scenario. Note that drain_all_stock() doesn't disable irq but only preemption.
CPU1 CPU2
stock->cached = memcgA (freed) drain_all_stock(memcgB) rcu_read_lock() memcg = CPU1's stock->cached (memcgA) (interrupted) refill_stock(memcgC) drain_stock(memcgA) stock->cached = memcgC stock->nr_pages += xxx (> 0) stock->nr_pages > 0 mem_cgroup_is_descendant(memcgA, memcgB) [UAF] rcu_read_unlock()
This problem is, unintenionally, fixed at 5.9, where commit 1a3e1f40962c ("mm: memcontrol: decouple reference counting from page accounting") adds memcg refcnt for stock. Therefore affected LTS versions include 4.19 and 5.4.
For 4.19, memcg's css offline process doesn't call drain_all_stock(). so it's easier for the released memcg to be left on the stock. For 5.4, although mem_cgroup_css_offline() does call drain_all_stock(), but the flushing could be skipped when stock->nr_pages happens to be 0, and besides the async draining could be delayed and take place after the UAF problem has happened.
Fix this problem by adding (and decreasing) memcg's refcnt when memcg is put onto (and removed from) stock, just like how commit 1a3e1f40962c ("mm: memcontrol: decouple reference counting from page accounting") does. After all, "being on the stock" is a kind of reference with regards to memcg. As such, it's guaranteed that a css on stock would not be freed.
What does prevent from the following?
refill_stock(memcgC) drain_all_stock(memcgB) drain_stock(memcgA) rcu_read_lock() css_put(old->css) memcgA = stock->cached mem_cgroup_is_descendant(memcgA, memcgB) UAF stock->cached = NULL
I think it's not a problem since refill_stock() has disabled irq before calling drain_stock():
refill_stock(memcgC) local_irq_save drain_stock(memcgA) css_put(old->css) <1> stock->cached = NULL local_irq_restore <2>
And since css_put(old->css) is an RCU free, memcgA would not be freed at <1> as it's still in grace period. The actual release of memcgA could happen only after irq is enabled (at <2>).
And for CPU2, the access to stock->cached in drain_all_stock() is protected by rcu_read_lock(), so from stock->cached we get either NULL, or a memcgA that is still not freed.
Please correct me if I have some wrong understanding to RCU.
Cc: stable@vger.kernel.org # 4.19 5.4 Fixes: cdec2e4265df ("memcg: coalesce charging via percpu storage") Signed-off-by: GONG, Ruiqi gongruiqi1@huawei.com
mm/memcontrol.c | 6 ++++++ 1 file changed, 6 insertions(+)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 5a366cf79821..8c04296df1c7 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2015,6 +2015,9 @@ static void drain_stock(struct memcg_stock_pcp *stock) { struct mem_cgroup *old = stock->cached;
- if (!old)
return;- if (stock->nr_pages) { page_counter_uncharge(&old->memory, stock->nr_pages); if (do_memsw_account())
@@ -2022,6 +2025,8 @@ static void drain_stock(struct memcg_stock_pcp *stock) css_put_many(&old->css, stock->nr_pages); stock->nr_pages = 0; }
- css_put(&old->css); stock->cached = NULL;
} @@ -2057,6 +2062,7 @@ static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages) stock = this_cpu_ptr(&memcg_stock); if (stock->cached != memcg) { /* reset if necessary */ drain_stock(stock);
css_get(&memcg->css);-- 2.25.1
On Wed 21-02-24 17:50:27, Gong Ruiqi wrote:
On 2024/02/21 16:38, Michal Hocko wrote:
On Wed 21-02-24 16:18:01, GONG, Ruiqi wrote:
commit 1a3e1f40962c445b997151a542314f3c6097f8c3 upstream.
I think it would be good to mention that this is only a partial backport and also explain why to do a partial rather than the full one.
Okay. I think to fix this problem we should add refcnt relation between memcg and stock, and since higher versions have achieved this, maybe it's better to use the same code and align with them. So I put a "commit xxx upstream" here, as requested in kernel docs[1]. So yes it's a partial backport as we only need the stock part.
I think it is sufficient to mention that this is a partial backport to minimize the fix to the bare minimum.
[...]
What does prevent from the following?
refill_stock(memcgC) drain_all_stock(memcgB) drain_stock(memcgA) rcu_read_lock() css_put(old->css) memcgA = stock->cached mem_cgroup_is_descendant(memcgA, memcgB) UAF stock->cached = NULL
I think it's not a problem since refill_stock() has disabled irq before calling drain_stock():
refill_stock(memcgC) local_irq_save drain_stock(memcgA) css_put(old->css) <1> stock->cached = NULL local_irq_restore <2>
And since css_put(old->css) is an RCU free, memcgA would not be freed at <1> as it's still in grace period. The actual release of memcgA could happen only after irq is enabled (at <2>).
And for CPU2, the access to stock->cached in drain_all_stock() is protected by rcu_read_lock(), so from stock->cached we get either NULL, or a memcgA that is still not freed.
Please correct me if I have some wrong understanding to RCU.
You are right. Thanks! IRQ disabling is there in one form or the other since db2ba40c277d ("mm: memcontrol: make per-cpu charge cache IRQ-safe for socket accounting") so 4.8+ is safe. Backports to older kernels would nee to pull this one as well.
Cc: stable@vger.kernel.org # 4.19 5.4 Fixes: cdec2e4265df ("memcg: coalesce charging via percpu storage") Signed-off-by: GONG, Ruiqi gongruiqi1@huawei.com
Acked-by: Michal Hocko mhocko@suse.com
Thanks!
On Wed 21-02-24 11:08:02, Michal Hocko wrote: [...]
You are right. Thanks! IRQ disabling is there in one form or the other since db2ba40c277d ("mm: memcontrol: make per-cpu charge cache IRQ-safe for socket accounting") so 4.8+ is safe. Backports to older kernels would nee to pull this one as well.
Scratch that. Prior to db2ba40c277d, we used to disable preemption via {get,put}_cpu_var and that should achive the same result.
On 2024/02/21 18:08, Michal Hocko wrote:
On Wed 21-02-24 17:50:27, Gong Ruiqi wrote:
On 2024/02/21 16:38, Michal Hocko wrote:
On Wed 21-02-24 16:18:01, GONG, Ruiqi wrote:
commit 1a3e1f40962c445b997151a542314f3c6097f8c3 upstream.
I think it would be good to mention that this is only a partial backport and also explain why to do a partial rather than the full one.
Okay. I think to fix this problem we should add refcnt relation between memcg and stock, and since higher versions have achieved this, maybe it's better to use the same code and align with them. So I put a "commit xxx upstream" here, as requested in kernel docs[1]. So yes it's a partial backport as we only need the stock part.
I think it is sufficient to mention that this is a partial backport to minimize the fix to the bare minimum.
Okay. Then I will send a v2 and add a paragraph to mention this.
[...]
On Wed, Feb 21, 2024 at 04:18:01PM +0800, GONG, Ruiqi wrote:
commit 1a3e1f40962c445b997151a542314f3c6097f8c3 upstream.
There was a kernel panic happened on an in-house environment running 3.10, and the same problem was reproduced on 4.19:
Now queued up, thanks!
greg k-h
On Wed 21-02-24 09:40:29, Greg KH wrote:
On Wed, Feb 21, 2024 at 04:18:01PM +0800, GONG, Ruiqi wrote:
commit 1a3e1f40962c445b997151a542314f3c6097f8c3 upstream.
There was a kernel panic happened on an in-house environment running 3.10, and the same problem was reproduced on 4.19:
Now queued up, thanks!
Give it some more time Greg, http://lkml.kernel.org/r/ZdW2gMajIw_cUN2-@tiehlicka
On Wed, Feb 21, 2024 at 09:48:05AM +0100, Michal Hocko wrote:
On Wed 21-02-24 09:40:29, Greg KH wrote:
On Wed, Feb 21, 2024 at 04:18:01PM +0800, GONG, Ruiqi wrote:
commit 1a3e1f40962c445b997151a542314f3c6097f8c3 upstream.
There was a kernel panic happened on an in-house environment running 3.10, and the same problem was reproduced on 4.19:
Now queued up, thanks!
Give it some more time Greg, http://lkml.kernel.org/r/ZdW2gMajIw_cUN2-@tiehlicka
Oops, now dropped, thanks!
greg k-h
On Wed 21-02-24 11:33:55, Greg KH wrote:
On Wed, Feb 21, 2024 at 09:48:05AM +0100, Michal Hocko wrote:
On Wed 21-02-24 09:40:29, Greg KH wrote:
On Wed, Feb 21, 2024 at 04:18:01PM +0800, GONG, Ruiqi wrote:
commit 1a3e1f40962c445b997151a542314f3c6097f8c3 upstream.
There was a kernel panic happened on an in-house environment running 3.10, and the same problem was reproduced on 4.19:
Now queued up, thanks!
Give it some more time Greg, http://lkml.kernel.org/r/ZdW2gMajIw_cUN2-@tiehlicka
Oops, now dropped, thanks!
Race conditions. The thing got resolved in the mean time. The patch is a partial backport, and I am OK with that. Now with my questions resolved this is good to know but a note about this being a partial backport in the changelog would be nice.
linux-stable-mirror@lists.linaro.org
-
Gong Ruiqi -
GONG, Ruiqi
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Greg KH -
Michal Hocko