From: Daniel Borkmann daniel@iogearbox.net
commit 0708a0afe291bdfe1386d74d5ec1f0c27e8b9168 upstream.
syzkaller was recently triggering an oversized kvmalloc() warning via xdp_umem_create().
The triggered warning was added back in 7661809d493b ("mm: don't allow oversized kvmalloc() calls"). The rationale for the warning for huge kvmalloc sizes was as a reaction to a security bug where the size was more than UINT_MAX but not everything was prepared to handle unsigned long sizes.
Anyway, the AF_XDP related call trace from this syzkaller report was:
kvmalloc include/linux/mm.h:806 [inline] kvmalloc_array include/linux/mm.h:824 [inline] kvcalloc include/linux/mm.h:829 [inline] xdp_umem_pin_pages net/xdp/xdp_umem.c:102 [inline] xdp_umem_reg net/xdp/xdp_umem.c:219 [inline] xdp_umem_create+0x6a5/0xf00 net/xdp/xdp_umem.c:252 xsk_setsockopt+0x604/0x790 net/xdp/xsk.c:1068 __sys_setsockopt+0x1fd/0x4e0 net/socket.c:2176 __do_sys_setsockopt net/socket.c:2187 [inline] __se_sys_setsockopt net/socket.c:2184 [inline] __x64_sys_setsockopt+0xb5/0x150 net/socket.c:2184 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x44/0xae
Björn mentioned that requests for >2GB allocation can still be valid:
The structure that is being allocated is the page-pinning accounting. AF_XDP has an internal limit of U32_MAX pages, which is *a lot*, but still fewer than what memcg allows (PAGE_COUNTER_MAX is a LONG_MAX/ PAGE_SIZE on 64 bit systems). [...]
I could just change from U32_MAX to INT_MAX, but as I stated earlier that has a hacky feeling to it. [...] From my perspective, the code isn't broken, with the memcg limits in consideration. [...]
Linus says:
[...] Pretty much every time this has come up, the kernel warning has shown that yes, the code was broken and there really wasn't a reason for doing allocations that big.
Of course, some people would be perfectly fine with the allocation failing, they just don't want the warning. I didn't want __GFP_NOWARN to shut it up originally because I wanted people to see all those cases, but these days I think we can just say "yeah, people can shut it up explicitly by saying 'go ahead and fail this allocation, don't warn about it'".
So enough time has passed that by now I'd certainly be ok with [it].
Thus allow call-sites to silence such userspace triggered splats if the allocation requests have __GFP_NOWARN. For xdp_umem_pin_pages()'s call to kvcalloc() this is already the case, so nothing else needed there.
Fixes: 7661809d493b ("mm: don't allow oversized kvmalloc() calls") Reported-by: syzbot+11421fbbff99b989670e@syzkaller.appspotmail.com Suggested-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Daniel Borkmann daniel@iogearbox.net Tested-by: syzbot+11421fbbff99b989670e@syzkaller.appspotmail.com Cc: Björn Töpel bjorn@kernel.org Cc: Magnus Karlsson magnus.karlsson@intel.com Cc: Willy Tarreau w@1wt.eu Cc: Andrew Morton akpm@linux-foundation.org Cc: Alexei Starovoitov ast@kernel.org Cc: Andrii Nakryiko andrii@kernel.org Cc: Jakub Kicinski kuba@kernel.org Cc: David S. Miller davem@davemloft.net Link: https://lore.kernel.org/bpf/CAJ+HfNhyfsT5cS_U9EC213ducHs9k9zNxX9+abqC0kTrPbQ... Link: https://lore.kernel.org/bpf/20211201202905.b9892171e3f5b9a60f9da251@linux-fo... Reviewed-by: Leon Romanovsky leonro@nvidia.com Ackd-by: Michal Hocko mhocko@suse.com Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- mm/util.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
--- a/mm/util.c +++ b/mm/util.c @@ -594,8 +594,10 @@ void *kvmalloc_node(size_t size, gfp_t f return ret;
/* Don't even allow crazy sizes */ - if (WARN_ON_ONCE(size > INT_MAX)) + if (unlikely(size > INT_MAX)) { + WARN_ON_ONCE(!(flags & __GFP_NOWARN)); return NULL; + }
return __vmalloc_node(size, 1, flags, node, __builtin_return_address(0));