Re: WARNING: CPU: 0 PID: 913 at fs/inode.c:275 drop_nlink+0x4b/0x50()

[OGAWA Hirofumi]

Vegard Nossum <vegard.nossum@xxxxxxxxxx> writes:

> On 11/23/2015 11:21 PM, Richard Weinberger wrote:
>> Am 23.11.2015 um 08:55 schrieb Vegard Nossum:
>>> With the attached vfat disk image (fuzzed), I get the following WARNING:
>>>
>>> WARNING: CPU: 0 PID: 913 at fs/inode.c:275 drop_nlink+0x4b/0x50()
> [...]
>>>
>>> To trigger it, you have to do a rename("/mnt/a/b/1", "/mnt/1"), where
>>> /mnt is your mountpoint.
>>
>> Not here. All I get is:
>> FAT-fs (ubdb): Corrupted directory (i_pos 244)
>>
>> Did you something before the rename()?
>
> No, nothing before the rename.
>
> Did you use mv to generate the rename()? Then you may have to do 'mv
> /mnt/a/b/1 /mnt/', otherwise it ends up doing rename("/mnt/a/b/1",
> "/mnt/1/1") which only shows the message you saw. Let me know if this helps.
>
> Thanks for having a look,

Can you try this one?
-- 
OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx>


[PATCH] fat: Add simple validation for directory inode


This detects simple corruption cases of directory, and try to avoid
further damage to user data.

And performance impact of this validation should be very low, or not
measurable.

Signed-off-by: OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx>
---

 fs/fat/inode.c |   22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff -puN fs/fat/inode.c~fat-validate-dir fs/fat/inode.c
--- linux/fs/fat/inode.c~fat-validate-dir	2015-11-26 06:31:39.666959958 +0900
+++ linux-hirofumi/fs/fat/inode.c	2015-11-26 06:31:39.670959945 +0900
@@ -449,6 +449,24 @@ static int fat_calc_dir_size(struct inod
 	return 0;
 }
 
+static int fat_validate_dir(struct inode *dir)
+{
+	struct super_block *sb = dir->i_sb;
+
+	if (dir->i_nlink < 2) {
+		/* Directory should have "."/".." entries at least. */
+		fat_fs_error(sb, "corrupted directory (invalid entries)");
+		return -EIO;
+	}
+	if (MSDOS_I(dir)->i_start == 0 ||
+	    MSDOS_I(dir)->i_start == MSDOS_SB(sb)->root_cluster) {
+		/* Directory should point valid cluster. */
+		fat_fs_error(sb, "corrupted directory (invalid i_start)");
+		return -EIO;
+	}
+	return 0;
+}
+
 /* doesn't deal with root inode */
 int fat_fill_inode(struct inode *inode, struct msdos_dir_entry *de)
 {
@@ -475,6 +493,10 @@ int fat_fill_inode(struct inode *inode,
 		MSDOS_I(inode)->mmu_private = inode->i_size;
 
 		set_nlink(inode, fat_subdirs(inode));
+
+		error = fat_validate_dir(inode);
+		if (error < 0)
+			return error;
 	} else { /* not a directory */
 		inode->i_generation |= 1;
 		inode->i_mode = fat_make_mode(sbi, de->attr,
_
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