c6f340a331
commit dacb5d8875cc6cd3a553363b4d6f06760fcbe70c upstream.
Steffen reported a TCP stream corruption for HTTP requests
served by the apache web-server using a cifs mount-point
and memory mapping the relevant file.
The root cause is quite similar to the one addressed by
commit 20eb4f29b602 ("net: fix sk_page_frag() recursion from
memory reclaim"). Here the nested access to the task page frag
is caused by a page fault on the (mmapped) user-space memory
buffer coming from the cifs file.
The page fault handler performs an smb transaction on a different
socket, inside the same process context. Since sk->sk_allaction
for such socket does not prevent the usage for the task_frag,
the nested allocation modify "under the hood" the page frag
in use by the outer sendmsg call, corrupting the stream.
The overall relevant stack trace looks like the following:
httpd 78268 [001] 3461630.850950: probe:tcp_sendmsg_locked:
ffffffff91461d91 tcp_sendmsg_locked+0x1
ffffffff91462b57 tcp_sendmsg+0x27
ffffffff9139814e sock_sendmsg+0x3e
ffffffffc06dfe1d smb_send_kvec+0x28
[...]
ffffffffc06cfaf8 cifs_readpages+0x213
ffffffff90e83c4b read_pages+0x6b
ffffffff90e83f31 __do_page_cache_readahead+0x1c1
ffffffff90e79e98 filemap_fault+0x788
ffffffff90eb0458 __do_fault+0x38
ffffffff90eb5280 do_fault+0x1a0
ffffffff90eb7c84 __handle_mm_fault+0x4d4
ffffffff90eb8093 handle_mm_fault+0xc3
ffffffff90c74f6d __do_page_fault+0x1ed
ffffffff90c75277 do_page_fault+0x37
ffffffff9160111e page_fault+0x1e
ffffffff9109e7b5 copyin+0x25
ffffffff9109eb40 _copy_from_iter_full+0xe0
ffffffff91462370 tcp_sendmsg_locked+0x5e0
ffffffff91462370 tcp_sendmsg_locked+0x5e0
ffffffff91462b57 tcp_sendmsg+0x27
ffffffff9139815c sock_sendmsg+0x4c
ffffffff913981f7 sock_write_iter+0x97
ffffffff90f2cc56 do_iter_readv_writev+0x156
ffffffff90f2dff0 do_iter_write+0x80
ffffffff90f2e1c3 vfs_writev+0xa3
ffffffff90f2e27c do_writev+0x5c
ffffffff90c042bb do_syscall_64+0x5b
ffffffff916000ad entry_SYSCALL_64_after_hwframe+0x65
The cifs filesystem rightfully sets sk_allocations to GFP_NOFS,
we can avoid the nesting using the sk page frag for allocation
lacking the __GFP_FS flag. Do not define an additional mm-helper
for that, as this is strictly tied to the sk page frag usage.
v1 -> v2:
- use a stricted sk_page_frag() check instead of reordering the
code (Eric)
Reported-by: Steffen Froemer <sfroemer@redhat.com>
Fixes: 5640f7685831 ("net: use a per task frag allocator")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
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https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.