6.12-stable review patch. If anyone has any objections, please let me know.
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From: Tetsuo Handa penguin-kernel@I-love.SAKURA.ne.jp
[ Upstream commit 34ab4c75588c07cca12884f2bf6b0347c7a13872 ]
syzbot is reporting that S_IFMT bits of inode->i_mode can become bogus when the S_IFMT bits of the 32bits "mode" field loaded from disk are corrupted or when the 32bits "attributes" field loaded from disk are corrupted.
A documentation says that BFS uses only lower 9 bits of the "mode" field. But I can't find an explicit explanation that the unused upper 23 bits (especially, the S_IFMT bits) are initialized with 0.
Therefore, ignore the S_IFMT bits of the "mode" field loaded from disk. Also, verify that the value of the "attributes" field loaded from disk is either BFS_VREG or BFS_VDIR (because BFS supports only regular files and the root directory).
Reported-by: syzbot+895c23f6917da440ed0d@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=895c23f6917da440ed0d Signed-off-by: Tetsuo Handa penguin-kernel@I-love.SAKURA.ne.jp Link: https://patch.msgid.link/fabce673-d5b9-4038-8287-0fd65d80203b@I-love.SAKURA.... Reviewed-by: Tigran Aivazian aivazian.tigran@gmail.com Signed-off-by: Christian Brauner brauner@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- fs/bfs/inode.c | 19 ++++++++++++++++++- 1 file changed, 18 insertions(+), 1 deletion(-)
diff --git a/fs/bfs/inode.c b/fs/bfs/inode.c index db81570c96375..ecf7f74779c6a 100644 --- a/fs/bfs/inode.c +++ b/fs/bfs/inode.c @@ -60,7 +60,19 @@ struct inode *bfs_iget(struct super_block *sb, unsigned long ino) off = (ino - BFS_ROOT_INO) % BFS_INODES_PER_BLOCK; di = (struct bfs_inode *)bh->b_data + off;
- inode->i_mode = 0x0000FFFF & le32_to_cpu(di->i_mode); + /* + * https://martin.hinner.info/fs/bfs/bfs-structure.html explains that + * BFS in SCO UnixWare environment used only lower 9 bits of di->i_mode + * value. This means that, although bfs_write_inode() saves whole + * inode->i_mode bits (which include S_IFMT bits and S_IS{UID,GID,VTX} + * bits), middle 7 bits of di->i_mode value can be garbage when these + * bits were not saved by bfs_write_inode(). + * Since we can't tell whether middle 7 bits are garbage, use only + * lower 12 bits (i.e. tolerate S_IS{UID,GID,VTX} bits possibly being + * garbage) and reconstruct S_IFMT bits for Linux environment from + * di->i_vtype value. + */ + inode->i_mode = 0x00000FFF & le32_to_cpu(di->i_mode); if (le32_to_cpu(di->i_vtype) == BFS_VDIR) { inode->i_mode |= S_IFDIR; inode->i_op = &bfs_dir_inops; @@ -70,6 +82,11 @@ struct inode *bfs_iget(struct super_block *sb, unsigned long ino) inode->i_op = &bfs_file_inops; inode->i_fop = &bfs_file_operations; inode->i_mapping->a_ops = &bfs_aops; + } else { + brelse(bh); + printf("Unknown vtype=%u %s:%08lx\n", + le32_to_cpu(di->i_vtype), inode->i_sb->s_id, ino); + goto error; }
BFS_I(inode)->i_sblock = le32_to_cpu(di->i_sblock);