From: Eric Dumazet edumazet@google.com
commit 915d975b2ffa58a14bfcf16fafe00c41315949ff upstream.
Blamed commit changed: ptr = kmalloc(size); if (ptr) size = ksize(ptr);
to: size = kmalloc_size_roundup(size); ptr = kmalloc(size);
This allowed various crash as reported by syzbot [1] and Kyle Zeng.
Problem is that if @size is bigger than 0x80000001, kmalloc_size_roundup(size) returns 2^32.
kmalloc_reserve() uses a 32bit variable (obj_size), so 2^32 is truncated to 0.
kmalloc(0) returns ZERO_SIZE_PTR which is not handled by skb allocations.
Following trace can be triggered if a netdev->mtu is set close to 0x7fffffff
We might in the future limit netdev->mtu to more sensible limit (like KMALLOC_MAX_SIZE).
This patch is based on a syzbot report, and also a report and tentative fix from Kyle Zeng.
[1] BUG: KASAN: user-memory-access in __build_skb_around net/core/skbuff.c:294 [inline] BUG: KASAN: user-memory-access in __alloc_skb+0x3c4/0x6e8 net/core/skbuff.c:527 Write of size 32 at addr 00000000fffffd10 by task syz-executor.4/22554
CPU: 1 PID: 22554 Comm: syz-executor.4 Not tainted 6.1.39-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/03/2023 Call trace: dump_backtrace+0x1c8/0x1f4 arch/arm64/kernel/stacktrace.c:279 show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:286 __dump_stack lib/dump_stack.c:88 [inline] dump_stack_lvl+0x120/0x1a0 lib/dump_stack.c:106 print_report+0xe4/0x4b4 mm/kasan/report.c:398 kasan_report+0x150/0x1ac mm/kasan/report.c:495 kasan_check_range+0x264/0x2a4 mm/kasan/generic.c:189 memset+0x40/0x70 mm/kasan/shadow.c:44 __build_skb_around net/core/skbuff.c:294 [inline] __alloc_skb+0x3c4/0x6e8 net/core/skbuff.c:527 alloc_skb include/linux/skbuff.h:1316 [inline] igmpv3_newpack+0x104/0x1088 net/ipv4/igmp.c:359 add_grec+0x81c/0x1124 net/ipv4/igmp.c:534 igmpv3_send_cr net/ipv4/igmp.c:667 [inline] igmp_ifc_timer_expire+0x1b0/0x1008 net/ipv4/igmp.c:810 call_timer_fn+0x1c0/0x9f0 kernel/time/timer.c:1474 expire_timers kernel/time/timer.c:1519 [inline] __run_timers+0x54c/0x710 kernel/time/timer.c:1790 run_timer_softirq+0x28/0x4c kernel/time/timer.c:1803 _stext+0x380/0xfbc ____do_softirq+0x14/0x20 arch/arm64/kernel/irq.c:79 call_on_irq_stack+0x24/0x4c arch/arm64/kernel/entry.S:891 do_softirq_own_stack+0x20/0x2c arch/arm64/kernel/irq.c:84 invoke_softirq kernel/softirq.c:437 [inline] __irq_exit_rcu+0x1c0/0x4cc kernel/softirq.c:683 irq_exit_rcu+0x14/0x78 kernel/softirq.c:695 el0_interrupt+0x7c/0x2e0 arch/arm64/kernel/entry-common.c:717 __el0_irq_handler_common+0x18/0x24 arch/arm64/kernel/entry-common.c:724 el0t_64_irq_handler+0x10/0x1c arch/arm64/kernel/entry-common.c:729 el0t_64_irq+0x1a0/0x1a4 arch/arm64/kernel/entry.S:584
Fixes: 12d6c1d3a2ad ("skbuff: Proactively round up to kmalloc bucket size") Reported-by: syzbot syzkaller@googlegroups.com Reported-by: Kyle Zeng zengyhkyle@gmail.com Signed-off-by: Eric Dumazet edumazet@google.com Cc: Kees Cook keescook@chromium.org Cc: Vlastimil Babka vbabka@suse.cz Signed-off-by: David S. Miller davem@davemloft.net [Ajay: Regenerated the patch for v6.1.y] Signed-off-by: Ajay Kaher akaher@vmware.com --- net/core/skbuff.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/net/core/skbuff.c b/net/core/skbuff.c index fb8d100..8dca4a7 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -428,11 +428,17 @@ static void *kmalloc_reserve(unsigned int *size, gfp_t flags, int node, bool *pfmemalloc) { bool ret_pfmemalloc = false; - unsigned int obj_size; + size_t obj_size; void *obj;
obj_size = SKB_HEAD_ALIGN(*size); - *size = obj_size = kmalloc_size_roundup(obj_size); + + obj_size = kmalloc_size_roundup(obj_size); + /* The following cast might truncate high-order bits of obj_size, this + * is harmless because kmalloc(obj_size >= 2^32) will fail anyway. + */ + *size = (unsigned int)obj_size; + /* * Try a regular allocation, when that fails and we're not entitled * to the reserves, fail.