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ext4: fix possible UAF when remounting r/o a mmp-protected file system

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After commit 618f003199 ("ext4: fix memory leak in
ext4_fill_super"), after the file system is remounted read-only, there
is a race where the kmmpd thread can exit, causing sbi->s_mmp_tsk to
point at freed memory, which the call to ext4_stop_mmpd() can trip
over.

Fix this by only allowing kmmpd() to exit when it is stopped via
ext4_stop_mmpd().

Link: https://lore.kernel.org/r/20210707002433.3719773-1-tytso@mit.edu
Reported-by: Ye Bin <yebin10@huawei.com>
Bug-Report-Link: <20210629143603.2166962-1-yebin10@huawei.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Jan Kara <jack@suse.cz>
This commit is contained in:
Theodore Ts'o 2021-07-02 12:45:02 -04:00
parent cd84bbbac1
commit 61bb4a1c41
2 changed files with 20 additions and 17 deletions
Download patch file Download diff file Expand all files Collapse all files

31
fs/ext4/mmp.c
View file

@ -156,7 +156,12 @@ static int kmmpd(void *data)
memcpy(mmp->mmp_nodename, init_utsname()->nodename, memcpy(mmp->mmp_nodename, init_utsname()->nodename,
sizeof(mmp->mmp_nodename)); sizeof(mmp->mmp_nodename));
while (!kthread_should_stop()) { while (!kthread_should_stop() && !sb_rdonly(sb)) {
if (!ext4_has_feature_mmp(sb)) {
ext4_warning(sb, "kmmpd being stopped since MMP feature"
" has been disabled.");
goto wait_to_exit;
}
if (++seq > EXT4_MMP_SEQ_MAX) if (++seq > EXT4_MMP_SEQ_MAX)
seq = 1; seq = 1;
@ -177,16 +182,6 @@ static int kmmpd(void *data)
failed_writes++; failed_writes++;
} }
if (!(le32_to_cpu(es->s_feature_incompat) &
EXT4_FEATURE_INCOMPAT_MMP)) {
ext4_warning(sb, "kmmpd being stopped since MMP feature"
" has been disabled.");
goto exit_thread;
}
if (sb_rdonly(sb))
break;
diff = jiffies - last_update_time; diff = jiffies - last_update_time;
if (diff < mmp_update_interval * HZ) if (diff < mmp_update_interval * HZ)
schedule_timeout_interruptible(mmp_update_interval * schedule_timeout_interruptible(mmp_update_interval *
@ -207,7 +202,7 @@ static int kmmpd(void *data)
ext4_error_err(sb, -retval, ext4_error_err(sb, -retval,
"error reading MMP data: %d", "error reading MMP data: %d",
retval); retval);
goto exit_thread; goto wait_to_exit;
} }
mmp_check = (struct mmp_struct *)(bh_check->b_data); mmp_check = (struct mmp_struct *)(bh_check->b_data);
@ -221,7 +216,7 @@ static int kmmpd(void *data)
ext4_error_err(sb, EBUSY, "abort"); ext4_error_err(sb, EBUSY, "abort");
put_bh(bh_check); put_bh(bh_check);
retval = -EBUSY; retval = -EBUSY;
goto exit_thread; goto wait_to_exit;
} }
put_bh(bh_check); put_bh(bh_check);
} }
@ -244,7 +239,13 @@ static int kmmpd(void *data)
retval = write_mmp_block(sb, bh); retval = write_mmp_block(sb, bh);
exit_thread: wait_to_exit:
while (!kthread_should_stop()) {
set_current_state(TASK_INTERRUPTIBLE);
if (!kthread_should_stop())
schedule();
}
set_current_state(TASK_RUNNING);
return retval; return retval;
} }
@ -391,5 +392,3 @@ failed:
brelse(bh); brelse(bh);
return 1; return 1;
} }

6
fs/ext4/super.c
View file

@ -5993,7 +5993,6 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data)
*/ */
ext4_mark_recovery_complete(sb, es); ext4_mark_recovery_complete(sb, es);
} }
ext4_stop_mmpd(sbi);
} else { } else {
/* Make sure we can mount this feature set readwrite */ /* Make sure we can mount this feature set readwrite */
if (ext4_has_feature_readonly(sb) || if (ext4_has_feature_readonly(sb) ||
@ -6107,6 +6106,9 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data)
if (!test_opt(sb, BLOCK_VALIDITY) && sbi->s_system_blks) if (!test_opt(sb, BLOCK_VALIDITY) && sbi->s_system_blks)
ext4_release_system_zone(sb); ext4_release_system_zone(sb);
if (!ext4_has_feature_mmp(sb) || sb_rdonly(sb))
ext4_stop_mmpd(sbi);
/* /*
* Some options can be enabled by ext4 and/or by VFS mount flag * Some options can be enabled by ext4 and/or by VFS mount flag
* either way we need to make sure it matches in both *flags and * either way we need to make sure it matches in both *flags and
@ -6140,6 +6142,8 @@ restore_opts:
for (i = 0; i < EXT4_MAXQUOTAS; i++) for (i = 0; i < EXT4_MAXQUOTAS; i++)
kfree(to_free[i]); kfree(to_free[i]);
#endif #endif
if (!ext4_has_feature_mmp(sb) || sb_rdonly(sb))
ext4_stop_mmpd(sbi);
kfree(orig_data); kfree(orig_data);
return err; return err;
} }