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| author | Roman Gushchin <klamm@yandex-team.ru> | 2015-10-12 16:33:44 +0300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2016-02-25 11:58:54 -0800 |
| commit | 7b54d4eea25df0cac10c9ccf353b36a62253547d (patch) | |
| tree | da14a7f14bad65f1177f7378a0b6bf37492e0a78 | |
| parent | b779a07997536eb821ec3cbcee18ab531adde6d4 (diff) | |
| download | lwn-7b54d4eea25df0cac10c9ccf353b36a62253547d.tar.gz lwn-7b54d4eea25df0cac10c9ccf353b36a62253547d.zip | |
fuse: break infinite loop in fuse_fill_write_pages()
commit 3ca8138f014a913f98e6ef40e939868e1e9ea876 upstream.
I got a report about unkillable task eating CPU. Further
investigation shows, that the problem is in the fuse_fill_write_pages()
function. If iov's first segment has zero length, we get an infinite
loop, because we never reach iov_iter_advance() call.
Fix this by calling iov_iter_advance() before repeating an attempt to
copy data from userspace.
A similar problem is described in 124d3b7041f ("fix writev regression:
pan hanging unkillable and un-straceable"). If zero-length segmend
is followed by segment with invalid address,
iov_iter_fault_in_readable() checks only first segment (zero-length),
iov_iter_copy_from_user_atomic() skips it, fails at second and
returns zero -> goto again without skipping zero-length segment.
Patch calls iov_iter_advance() before goto again: we'll skip zero-length
segment at second iteraction and iov_iter_fault_in_readable() will detect
invalid address.
Special thanks to Konstantin Khlebnikov, who helped a lot with the commit
description.
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Maxim Patlasov <mpatlasov@parallels.com>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: Roman Gushchin <klamm@yandex-team.ru>
Signed-off-by: Miklos Szeredi <miklos@szeredi.hu>
Fixes: ea9b9907b82a ("fuse: implement perform_write")
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | fs/fuse/file.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/fs/fuse/file.c b/fs/fuse/file.c index d8a60270581c..f9785e3c63ac 100644 --- a/fs/fuse/file.c +++ b/fs/fuse/file.c @@ -1006,6 +1006,7 @@ static ssize_t fuse_fill_write_pages(struct fuse_req *req, tmp = iov_iter_copy_from_user_atomic(page, ii, offset, bytes); flush_dcache_page(page); + iov_iter_advance(ii, tmp); if (!tmp) { unlock_page(page); page_cache_release(page); @@ -1018,7 +1019,6 @@ static ssize_t fuse_fill_write_pages(struct fuse_req *req, req->page_descs[req->num_pages].length = tmp; req->num_pages++; - iov_iter_advance(ii, tmp); count += tmp; pos += tmp; offset += tmp; |