Commit 913e027c authored Feb 10, 2015 by Dmitry Monakhov Committed by Linus Torvalds Feb 10, 2015

fsioctl.c: make generic_block_fiemap() signal-tolerant



__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>

parent 99b8874e

Documentation/filesystems/fiemap.txt

+2 −1

Original line number	Diff line number	Diff line
		@@ -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

fs/ioctl.c

+5 −0

Original line number	Diff line number	Diff line
		@@ -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 */