ext4: prevent right-shifting extents beyond EXT_MAX_BLOCKS
commit 349fa7d6e1935f49bf4161c4900711b2989180a9 upstream.
During the "insert range" fallocate operation, extents starting at the
range offset are shifted "right" (to a higher file offset) by the range
length. But, as shown by syzbot, it's not validated that this doesn't
cause extents to be shifted beyond EXT_MAX_BLOCKS. In that case
->ee_block can wrap around, corrupting the extent tree.
Fix it by returning an error if the space between the end of the last
extent and EXT4_MAX_BLOCKS is smaller than the range being inserted.
This bug can be reproduced by running the following commands when the
current directory is on an ext4 filesystem with a 4k block size:
fallocate -l 8192 file
fallocate --keep-size -o 0xfffffffe000 -l 4096 -n file
fallocate --insert-range -l 8192 file
Then after unmounting the filesystem, e2fsck reports corruption.
Reported-by: syzbot+06c885be0edcdaeab40c@syzkaller.appspotmail.com
Fixes: 331573febb6a ("ext4: Add support FALLOC_FL_INSERT_RANGE for fallocate")
Cc: stable@vger.kernel.org # v4.2+
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 1a0c571..63c702b 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -5356,8 +5356,9 @@
stop = le32_to_cpu(extent->ee_block);
/*
- * In case of left shift, Don't start shifting extents until we make
- * sure the hole is big enough to accommodate the shift.
+ * For left shifts, make sure the hole on the left is big enough to
+ * accommodate the shift. For right shifts, make sure the last extent
+ * won't be shifted beyond EXT_MAX_BLOCKS.
*/
if (SHIFT == SHIFT_LEFT) {
path = ext4_find_extent(inode, start - 1, &path,
@@ -5377,9 +5378,14 @@
if ((start == ex_start && shift > ex_start) ||
(shift > start - ex_end)) {
- ext4_ext_drop_refs(path);
- kfree(path);
- return -EINVAL;
+ ret = -EINVAL;
+ goto out;
+ }
+ } else {
+ if (shift > EXT_MAX_BLOCKS -
+ (stop + ext4_ext_get_actual_len(extent))) {
+ ret = -EINVAL;
+ goto out;
}
}