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>

1 files changed, 5 insertions, 0 deletions

diff --git a/fs/ioctl.c b/fs/ioctl.c
index 214c3c11fbc2..5d01d2638ca5 100644
--- a/fs/ioctl.c
+++ b/fs/ioctl.c
@@ -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 */