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fsioctl.c: make generic_block_fiemap() signal-tolerant

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__generic_block_fiemap may spin very long time for large sparse files.

Without this patch an unprivileged user may abuse system resources simply
by spawning a vast number of unkilable busyloops (works on ext2/ext3):

  truncate --size 1T test
  for ((i=0;i<1024;i++))
  do
         filefrag test > /dev/null &
  done

Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Dmitry Monakhov 2015-02-10 14:09:29 -08:00 committed by Linus Torvalds
parent 99b8874e79
commit 913e027ca1
2 changed files with 7 additions and 1 deletions
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3
Documentation/filesystems/fiemap.txt
View File

@ -196,7 +196,8 @@ struct fiemap_extent_info {
};
It is intended that the file system should not need to access any of this
structure directly.
structure directly. Filesystem handlers should be tolerant to signals and return
EINTR once fatal signal received.
Flag checking should be done at the beginning of the ->fiemap callback via the

5
fs/ioctl.c
View File

@ -379,6 +379,11 @@ int __generic_block_fiemap(struct inode *inode,
past_eof = true;
}
cond_resched();
if (fatal_signal_pending(current)) {
ret = -EINTR;
break;
}
} while (1);
/* If ret is 1 then we just hit the end of the extent array */