libext2fs: fix crash in ext2fs_open2() on Big Endian systems
Commit e6069a05: ("Teach ext2fs_open2() to honor the
EXT2_FLAG_SUPER_ONLY flag") changed how the function
ext2fs_group_desc() handled a request for a gdp pointer for a group
larger than the number of groups in the file system; it now returns
NULL, instead of returning a pointer beyond the end of the array.
Previously, the ext2fs_open2() function would swap all of the block
group descriptors in a block, even if they are beyond the end of the
file system. This was OK, since we were not overrunning the allocated
memory, since it was rounded to a block boundary. But now that
ext2fs_group_desc() would return NULL for those gdp, it would cause
ext2fs_open2(), when it was byte swapping the block group descriptors
on Big Endian systems, to dereference a null pointer and crash.
This commit adds a NULL pointer check to avoid byte swapping those
block group descriptors in a bg descriptor block, but which are beyond
the end of the file system, to address this crash.
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reported-by: Anatoly Pugachev <matorola@gmail.com>
diff --git a/lib/ext2fs/openfs.c b/lib/ext2fs/openfs.c
index ec2d6cb..3331452 100644
--- a/lib/ext2fs/openfs.c
+++ b/lib/ext2fs/openfs.c
@@ -435,7 +435,8 @@
gdp = (struct ext2_group_desc *) dest;
for (j=0; j < groups_per_block*first_meta_bg; j++) {
gdp = ext2fs_group_desc(fs, fs->group_desc, j);
- ext2fs_swap_group_desc2(fs, gdp);
+ if (gdp)
+ ext2fs_swap_group_desc2(fs, gdp);
}
#endif
dest += fs->blocksize*first_meta_bg;
@@ -455,7 +456,8 @@
for (j=0; j < groups_per_block; j++) {
gdp = ext2fs_group_desc(fs, fs->group_desc,
i * groups_per_block + j);
- ext2fs_swap_group_desc2(fs, gdp);
+ if (gdp)
+ ext2fs_swap_group_desc2(fs, gdp);
}
#endif
dest += fs->blocksize;
