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ext4: fix hole length detection in ext4_ind_map_blocks() 

When ext4_ind_map_blocks() computes a length of a hole, it doesn't count
with the fact that mapped offset may be somewhere in the middle of the
completely empty subtree. In such case it will return too large length
of the hole which then results in lseek(SEEK_DATA) to end up returning
an incorrect offset beyond the end of the hole.

Fix the problem by correctly taking offset within a subtree into account
when computing a length of a hole.

Fixes: facab4d971
CC: stable@vger.kernel.org
Reported-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
Jan Kara 2018-05-12 19:55:00 -04:00 committed by Theodore Ts'o
parent 736dedbb1a
commit 2ee3ee06a8
1 changed files with 10 additions and 4 deletions
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14
fs/ext4/indirect.c
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@ -561,10 +561,16 @@ int ext4_ind_map_blocks(handle_t *handle, struct inode *inode,
unsigned epb = inode->i_sb->s_blocksize / sizeof(u32);
int i;
/* Count number blocks in a subtree under 'partial' */
count = 1;
for (i = 0; partial + i != chain + depth - 1; i++)
count *= epb;
/*
* Count number blocks in a subtree under 'partial'. At each
* level we count number of complete empty subtrees beyond
* current offset and then descend into the subtree only
* partially beyond current offset.
*/
count = 0;
for (i = partial - chain + 1; i < depth; i++)
count = count * epb + (epb - offsets[i] - 1);
count++;
/* Fill in size of a hole we found */
map->m_pblk = 0;
map->m_len = min_t(unsigned int, map->m_len, count);