New: EXT4_IOC_MIGRATE is dangerous on directories

https://bugzilla.kernel.org/show_bug.cgi?id=40512

Summary: EXT4_IOC_MIGRATE is dangerous on directories
Product: File System
Version: 2.5
Kernel Version: 2.6.39
Platform: All
OS/Version: Linux
Tree: Mainline
Status: NEW
Severity: high
Priority: P1
Component: ext4
AssignedTo: [email protected]
ReportedBy: [email protected]
Regression: No

Using EXT4_IOC_MIGRATE on a non-extent directory seems to have terrible consequences. Consider the following example. "dir" is a old directory without extents.

$ ls -la dir/
total 12
drwxr-xr-x  2 benjamin benjamin 4096 Aug  3 20:42 .
drwxr-xr-x 47 benjamin benjamin 4096 Aug  3 20:42 ..
-rw-r-----  1 benjamin benjamin    7 Aug  3 20:42 something.txt
$ cat migrate.c
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>

int
main(int argc, char **argv)

{
    const char *fn = argv[1];
    int fd, ret;

    fd = open(fn, O_RDONLY);
    /* This invokes EXT4_IOC_MIGRATE. */
    ret = ioctl(fd, 0x6609);
    close(fd);
    if (ret < 0) {
        fprintf(stderr, "ioctl failed\n");
        return 1;
    }
    printf("Migration successful?\n");
    return 0;
}
$ gcc -o migrate migrate.c
$ ./migrate dir
Migration successful?
$ ls -la dir
total 0 # !!!!!!!!!!!!!!

Also, we why are you allowed to migrate stuff with only O_RDONLY access?

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https://bugzilla.kernel.org/show_bug.cgi?id=40512

Tao Ma <[email protected]> changed:

What |Removed |Added
----------------------------------------------------------------------------
CC| |[email protected]

--- Comment #1 from Tao Ma <[email protected]> 2011-08-04 06:31:42 --- Tested with 3.0, and it works here. git log shows that a possible fix should be 74e4e6db3 which is included in 3.0.

One thing you could confirm is to run:
debugfs 'stat dir' /dev/sdx
to see whether the EXTENTS flags is set or not. If it isn't set, it should be the root cause.

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https://bugzilla.kernel.org/show_bug.cgi?id=40512

--- Comment #2 from Benjamin Peterson <[email protected]> 2011-08-04 13:26:33 --- When I ran e2fsck on the partition, it reported EXTENTS_FL was not set.

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https://bugzilla.kernel.org/show_bug.cgi?id=40512

Benjamin Peterson <[email protected]> changed:

What |Removed |Added
----------------------------------------------------------------------------

             Status|NEW                         |RESOLVED
         Resolution|                            |CODE_FIX

--- Comment #3 from Benjamin Peterson <[email protected]> 2012-01-17 14:10:10 --- Indeed, it is now fixed. Thanks.

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