57 lines
2.1 KiB
Diff
57 lines
2.1 KiB
Diff
From: Roman Gushchin <klamm@yandex-team.ru>
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Date: Mon, 12 Oct 2015 16:33:44 +0300
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Subject: fuse: break infinite loop in fuse_fill_write_pages()
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Origin: https://git.kernel.org/linus/3ca8138f014a913f98e6ef40e939868e1e9ea876
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I got a report about unkillable task eating CPU. Further
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investigation shows, that the problem is in the fuse_fill_write_pages()
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function. If iov's first segment has zero length, we get an infinite
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loop, because we never reach iov_iter_advance() call.
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Fix this by calling iov_iter_advance() before repeating an attempt to
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copy data from userspace.
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A similar problem is described in 124d3b7041f ("fix writev regression:
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pan hanging unkillable and un-straceable"). If zero-length segmend
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is followed by segment with invalid address,
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iov_iter_fault_in_readable() checks only first segment (zero-length),
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iov_iter_copy_from_user_atomic() skips it, fails at second and
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returns zero -> goto again without skipping zero-length segment.
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Patch calls iov_iter_advance() before goto again: we'll skip zero-length
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segment at second iteraction and iov_iter_fault_in_readable() will detect
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invalid address.
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Special thanks to Konstantin Khlebnikov, who helped a lot with the commit
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description.
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Cc: Andrew Morton <akpm@linux-foundation.org>
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Cc: Maxim Patlasov <mpatlasov@parallels.com>
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Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
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Signed-off-by: Roman Gushchin <klamm@yandex-team.ru>
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Signed-off-by: Miklos Szeredi <miklos@szeredi.hu>
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Fixes: ea9b9907b82a ("fuse: implement perform_write")
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Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
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---
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fs/fuse/file.c | 2 +-
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1 file changed, 1 insertion(+), 1 deletion(-)
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--- a/fs/fuse/file.c
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+++ b/fs/fuse/file.c
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@@ -1049,6 +1049,7 @@ static ssize_t fuse_fill_write_pages(str
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tmp = iov_iter_copy_from_user_atomic(page, ii, offset, bytes);
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flush_dcache_page(page);
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+ iov_iter_advance(ii, tmp);
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if (!tmp) {
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unlock_page(page);
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page_cache_release(page);
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@@ -1061,7 +1062,6 @@ static ssize_t fuse_fill_write_pages(str
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req->page_descs[req->num_pages].length = tmp;
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req->num_pages++;
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- iov_iter_advance(ii, tmp);
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count += tmp;
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pos += tmp;
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offset += tmp;
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