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Date: Wed, 25 Jan 2023 10:16:13 +0100
From: Jan Kara <jack@...e.cz>
To: Shigeru Yoshida <syoshida@...hat.com>
Cc: jack@...e.com, linux-kernel@...r.kernel.org,
syzbot+aebf90eea2671c43112a@...kaller.appspotmail.com
Subject: Re: [PATCH -next] udf: Fix a race condition between udf_rename() and
udf_expand_dir_adinicb()
On Wed 25-01-23 02:30:15, Shigeru Yoshida wrote:
> syzbot reported a general fault in udf_filter_write_fi() [1]. This
> causes a stack trace like below:
>
> general protection fault, probably for non-canonical address 0xdffffc0000000005: 0000 [#1] PREEMPT SMP KASAN
> KASAN: null-ptr-deref in range [0x0000000000000028-0x000000000000002f]
> CPU: 0 PID: 5127 Comm: syz-executor298 Not tainted 6.2.0-rc3-next-20230112-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
> RIP: 0010:udf_fiiter_write_fi+0x14e/0x9d0 fs/udf/directory.c:402
> ...
> Call Trace:
> <TASK>
> udf_rename+0x69d/0xb80 fs/udf/namei.c:874
> vfs_rename+0x1162/0x1a90 fs/namei.c:4780
> do_renameat2+0xb22/0xc30 fs/namei.c:4931
> __do_sys_rename fs/namei.c:4977 [inline]
> __se_sys_rename fs/namei.c:4975 [inline]
> __x64_sys_rename+0x81/0xa0 fs/namei.c:4975
> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
> entry_SYSCALL_64_after_hwframe+0x63/0xcd
>
> The cause of this issue is a race condition between udf_rename() and
> udf_expand_dir_adinicb().
>
> If udf_rename() and udf_expand_dir_adinicb() run concurrently,
> iinfo->i_alloc_type can be changed by udf_expand_dir_adinicb() while
> udf_rename() is running. This causes NULL pointer dereference for
> iter->bh[0]->b_data in udf_fiiter_write_fi().
>
> Link: https://syzkaller.appspot.com/bug?id=2811e6cdd35ea1df1fa2ef31b8d92c6408aa15d2 [1]
> Reported-by: syzbot+aebf90eea2671c43112a@...kaller.appspotmail.com
> Signed-off-by: Shigeru Yoshida <syoshida@...hat.com>
Thanks for the patch but I have already fixed the bug in a patch I've
posted here [1]. A cleaner fix is actually to use i_rwsem to protect moved
directory from other modifications (which is what I did).
[1] https://lore.kernel.org/all/20230124121814.25951-14-jack@suse.cz
Honza
> ---
> fs/udf/namei.c | 35 ++++++++++++++++++++++++-----------
> 1 file changed, 24 insertions(+), 11 deletions(-)
>
> diff --git a/fs/udf/namei.c b/fs/udf/namei.c
> index 06f066ba3072..5048652c6cd4 100644
> --- a/fs/udf/namei.c
> +++ b/fs/udf/namei.c
> @@ -149,6 +149,8 @@ static struct buffer_head *udf_expand_dir_adinicb(struct inode *inode,
> uint8_t *impuse;
> int ret;
>
> + down_write(&iinfo->i_data_sem);
> +
> if (UDF_QUERY_FLAG(inode->i_sb, UDF_FLAG_USE_SHORT_AD))
> alloctype = ICBTAG_FLAG_AD_SHORT;
> else
> @@ -157,7 +159,7 @@ static struct buffer_head *udf_expand_dir_adinicb(struct inode *inode,
> if (!inode->i_size) {
> iinfo->i_alloc_type = alloctype;
> mark_inode_dirty(inode);
> - return NULL;
> + goto out;
> }
>
> /* alloc block, and copy data to it */
> @@ -165,15 +167,15 @@ static struct buffer_head *udf_expand_dir_adinicb(struct inode *inode,
> iinfo->i_location.partitionReferenceNum,
> iinfo->i_location.logicalBlockNum, err);
> if (!(*block))
> - return NULL;
> + goto out;
> newblock = udf_get_pblock(inode->i_sb, *block,
> iinfo->i_location.partitionReferenceNum,
> 0);
> if (!newblock)
> - return NULL;
> + goto out;
> dbh = udf_tgetblk(inode->i_sb, newblock);
> if (!dbh)
> - return NULL;
> + goto out;
> lock_buffer(dbh);
> memcpy(dbh->b_data, iinfo->i_data, inode->i_size);
> memset(dbh->b_data + inode->i_size, 0,
> @@ -197,7 +199,7 @@ static struct buffer_head *udf_expand_dir_adinicb(struct inode *inode,
> if (ret < 0) {
> *err = ret;
> udf_free_blocks(inode->i_sb, inode, &eloc, 0, 1);
> - return NULL;
> + goto out;
> }
> mark_inode_dirty(inode);
>
> @@ -213,6 +215,8 @@ static struct buffer_head *udf_expand_dir_adinicb(struct inode *inode,
> impuse = NULL;
> udf_fiiter_write_fi(&iter, impuse);
> }
> + up_write(&iinfo->i_data_sem);
> +
> /*
> * We don't expect the iteration to fail as the directory has been
> * already verified to be correct
> @@ -221,6 +225,9 @@ static struct buffer_head *udf_expand_dir_adinicb(struct inode *inode,
> udf_fiiter_release(&iter);
>
> return dbh;
> +out:
> + up_write(&iinfo->i_data_sem);
> + return NULL;
> }
>
> static int udf_fiiter_add_entry(struct inode *dir, struct dentry *dentry,
> @@ -766,6 +773,7 @@ static int udf_rename(struct mnt_idmap *idmap, struct inode *old_dir,
> bool has_diriter = false;
> int retval;
> struct kernel_lb_addr tloc;
> + struct udf_inode_info *old_iinfo = UDF_I(old_inode);
>
> if (flags & ~RENAME_NOREPLACE)
> return -EINVAL;
> @@ -780,11 +788,13 @@ static int udf_rename(struct mnt_idmap *idmap, struct inode *old_dir,
> goto out_oiter;
> }
>
> + down_read(&old_iinfo->i_data_sem);
> +
> if (S_ISDIR(old_inode->i_mode)) {
> if (new_inode) {
> retval = -ENOTEMPTY;
> if (!empty_dir(new_inode))
> - goto out_oiter;
> + goto out_unlock;
> }
> retval = udf_fiiter_find_entry(old_inode, &dotdot_name,
> &diriter);
> @@ -795,7 +805,7 @@ static int udf_rename(struct mnt_idmap *idmap, struct inode *old_dir,
> retval = -EFSCORRUPTED;
> }
> if (retval)
> - goto out_oiter;
> + goto out_unlock;
> has_diriter = true;
> tloc = lelb_to_cpu(diriter.fi.icb.extLocation);
> if (udf_get_lb_pblock(old_inode->i_sb, &tloc, 0) !=
> @@ -805,25 +815,25 @@ static int udf_rename(struct mnt_idmap *idmap, struct inode *old_dir,
> "directory (ino %lu) has parent entry pointing to another inode (%lu != %u)\n",
> old_inode->i_ino, old_dir->i_ino,
> udf_get_lb_pblock(old_inode->i_sb, &tloc, 0));
> - goto out_oiter;
> + goto out_unlock;
> }
> }
>
> retval = udf_fiiter_find_entry(new_dir, &new_dentry->d_name, &niter);
> if (retval && retval != -ENOENT)
> - goto out_oiter;
> + goto out_unlock;
> /* Entry found but not passed by VFS? */
> if (!retval && !new_inode) {
> retval = -EFSCORRUPTED;
> udf_fiiter_release(&niter);
> - goto out_oiter;
> + goto out_unlock;
> }
> /* Entry not found? Need to add one... */
> if (retval) {
> udf_fiiter_release(&niter);
> retval = udf_fiiter_add_entry(new_dir, new_dentry, &niter);
> if (retval)
> - goto out_oiter;
> + goto out_unlock;
> }
>
> /*
> @@ -882,7 +892,10 @@ static int udf_rename(struct mnt_idmap *idmap, struct inode *old_dir,
> mark_inode_dirty(new_dir);
> }
> }
> + up_read(&old_iinfo->i_data_sem);
> return 0;
> +out_unlock:
> + up_read(&old_iinfo->i_data_sem);
> out_oiter:
> if (has_diriter)
> udf_fiiter_release(&diriter);
> --
> 2.39.0
>
--
Jan Kara <jack@...e.com>
SUSE Labs, CR
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