On Fri 27-09-24 21:33:29, libaokun@huaweicloud.com wrote:

From: Baokun Li libaokun1@huawei.com

Wesley reported an issue:

================================================================== EXT4-fs (dm-5): resizing filesystem from 7168 to 786432 blocks ------------[ cut here ]------------ kernel BUG at fs/ext4/resize.c:324! CPU: 9 UID: 0 PID: 3576 Comm: resize2fs Not tainted 6.11.0+ #27 RIP: 0010:ext4_resize_fs+0x1212/0x12d0 Call Trace: __ext4_ioctl+0x4e0/0x1800 ext4_ioctl+0x12/0x20 __x64_sys_ioctl+0x99/0xd0 x64_sys_call+0x1206/0x20d0 do_syscall_64+0x72/0x110 entry_SYSCALL_64_after_hwframe+0x76/0x7e ==================================================================

While reviewing the patch, Honza found that when adjusting resize_bg in alloc_flex_gd(), it was possible for flex_gd->resize_bg to be bigger than flexbg_size.

The reproduction of the problem requires the following:

o_group = flexbg_size * 2 * n; o_size = (o_group + 1) * group_size; n_group: [o_group + flexbg_size, o_group + flexbg_size * 2) o_size = (n_group + 1) * group_size;

Take n=0,flexbg_size=16 as an example:

          last:15

|o---------------|--------------n-| o_group:0 resize to n_group:30

The corresponding reproducer is:

img=test.img truncate -s 600M $img mkfs.ext4 -F $img -b 1024 -G 16 8M dev=`losetup -f --show $img` mkdir -p /tmp/test mount $dev /tmp/test resize2fs $dev 248M

Delete the problematic plus 1 to fix the issue, and add a WARN_ON_ONCE() to prevent the issue from happening again.

Reported-by: Wesley Hershberger wesley.hershberger@canonical.com Closes: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2081231 Reported-by: Stéphane Graber stgraber@stgraber.org Closes: https://lore.kernel.org/all/20240925143325.518508-1-aleksandr.mikhalitsyn@ca... Tested-by: Alexander Mikhalitsyn aleksandr.mikhalitsyn@canonical.com Tested-by: Eric Sandeen sandeen@redhat.com Fixes: 665d3e0af4d3 ("ext4: reduce unnecessary memory allocation in alloc_flex_gd()") Cc: stable@vger.kernel.org Signed-off-by: Baokun Li libaokun1@huawei.com

Looks good. Feel free to add:

Reviewed-by: Jan Kara jack@suse.cz

Honza

---

Changes since v1:

• Add missing WARN_ON_ONCE().
• Correct the comment of alloc_flex_gd().

fs/ext4/resize.c | 18 ++++++++++-------- 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c index e04eb08b9060..a2704f064361 100644 --- a/fs/ext4/resize.c +++ b/fs/ext4/resize.c @@ -230,8 +230,8 @@ struct ext4_new_flex_group_data { #define MAX_RESIZE_BG 16384 /*

• • alloc_flex_gd() allocates a ext4_new_flex_group_data with size of
• • @flexbg_size.

• • alloc_flex_gd() allocates an ext4_new_flex_group_data that satisfies the
• • resizing from @o_group to @n_group, its size is typically @flexbg_size.
  • Returns NULL on failure otherwise address of the allocated structure.
  */

@@ -239,25 +239,27 @@ static struct ext4_new_flex_group_data *alloc_flex_gd(unsigned int flexbg_size, ext4_group_t o_group, ext4_group_t n_group) { ext4_group_t last_group;

• unsigned int max_resize_bg; struct ext4_new_flex_group_data *flex_gd;

flex_gd = kmalloc(sizeof(*flex_gd), GFP_NOFS); if (flex_gd == NULL) goto out3;

• if (unlikely(flexbg_size > MAX_RESIZE_BG))

• flex_gd->resize_bg = MAX_RESIZE_BG;
  

• else

• flex_gd->resize_bg = flexbg_size;
  

• max_resize_bg = umin(flexbg_size, MAX_RESIZE_BG);
• flex_gd->resize_bg = max_resize_bg;

/* Avoid allocating large 'groups' array if not needed */ last_group = o_group | (flex_gd->resize_bg - 1); if (n_group <= last_group)

• flex_gd->resize_bg = 1 << fls(n_group - o_group + 1);
  

• flex_gd->resize_bg = 1 << fls(n_group - o_group);
  

  else if (n_group - last_group < flex_gd->resize_bg)

• flex_gd->resize_bg = 1 << max(fls(last_group - o_group + 1),
  

• flex_gd->resize_bg = 1 << max(fls(last_group - o_group),
  		      fls(n_group - last_group));
  

• if (WARN_ON_ONCE(flex_gd->resize_bg > max_resize_bg))

• flex_gd->resize_bg = max_resize_bg;
  

• flex_gd->groups = kmalloc_array(flex_gd->resize_bg, sizeof(struct ext4_new_group_data), GFP_NOFS);

-- 2.39.2