3.16.55-rc1 review patch. If anyone has any objections, please let me know.
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From: Nikolay Borisov nborisov@suse.com
commit c8bcbfbd239ed60a6562964b58034ac8a25f4c31 upstream.
The name char array passed to btrfs_search_path_in_tree is of size BTRFS_INO_LOOKUP_PATH_MAX (4080). So the actual accessible char indexes are in the range of [0, 4079]. Currently the code uses the define but this represents an off-by-one.
Implications:
Size of btrfs_ioctl_ino_lookup_args is 4096, so the new byte will be written to extra space, not some padding that could be provided by the allocator.
btrfs-progs store the arguments on stack, but kernel does own copy of the ioctl buffer and the off-by-one overwrite does not affect userspace, but the ending 0 might be lost.
Kernel ioctl buffer is allocated dynamically so we're overwriting somebody else's memory, and the ioctl is privileged if args.objectid is not 256. Which is in most cases, but resolving a subvolume stored in another directory will trigger that path.
Before this patch the buffer was one byte larger, but then the -1 was not added.
Fixes: ac8e9819d71f907 ("Btrfs: add search and inode lookup ioctls") Signed-off-by: Nikolay Borisov nborisov@suse.com Reviewed-by: David Sterba dsterba@suse.com [ added implications ] Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Ben Hutchings ben@decadent.org.uk --- fs/btrfs/ioctl.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/fs/btrfs/ioctl.c +++ b/fs/btrfs/ioctl.c @@ -2253,7 +2253,7 @@ static noinline int btrfs_search_path_in if (!path) return -ENOMEM;
- ptr = &name[BTRFS_INO_LOOKUP_PATH_MAX]; + ptr = &name[BTRFS_INO_LOOKUP_PATH_MAX - 1];
key.objectid = tree_id; key.type = BTRFS_ROOT_ITEM_KEY;