[PATCH v3] ocfs2: validate group add input before caching

[ZhengYuan Huang <gality369@gmail.com>]

[BUG]
OCFS2_IOC_GROUP_ADD can trigger a BUG_ON in
ocfs2_set_new_buffer_uptodate():

kernel BUG at fs/ocfs2/uptodate.c:509!
Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI
RIP: 0010:ocfs2_set_new_buffer_uptodate+0x194/0x1e0 fs/ocfs2/uptodate.c:509
Code: ffffe88f 42b9fe4c 89e64889 dfe8b4df
Call Trace:
 ocfs2_group_add+0x3f1/0x1510 fs/ocfs2/resize.c:507
 ocfs2_ioctl+0x309/0x6e0 fs/ocfs2/ioctl.c:887
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl fs/ioctl.c:583 [inline]
 __x64_sys_ioctl+0x197/0x1e0 fs/ioctl.c:583
 x64_sys_call+0x1144/0x26a0 arch/x86/include/generated/asm/syscalls_64.h:17
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x93/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x76/0x7e
RIP: 0033:0x7bbfb55a966d

[CAUSE]
ocfs2_group_add() calls ocfs2_set_new_buffer_uptodate() on a
user-controlled group block before ocfs2_verify_group_and_input()
validates that block number. That helper is only valid for newly
allocated metadata and asserts that the block is not already present in
the chosen metadata cache. The code also uses INODE_CACHE(inode) even
though the group descriptor belongs to main_bm_inode and later journal
accesses use that cache context instead.

[FIX]
Validate the on-disk group descriptor before caching it, then add it to
the metadata cache tracked by INODE_CACHE(main_bm_inode). Keep the
validation failure path separate from the later cleanup path so we only
remove the buffer from that cache after it has actually been inserted.
This keeps the group buffer lifetime consistent across validation,
journaling, and cleanup.

Fixes: 7909f2bf8353 ("[PATCH 2/2] ocfs2: Implement group add for online resize")
Signed-off-by: ZhengYuan Huang <gality369@gmail.com>
---
v3:
- keep out_free_group_bh as the brelse() label
- add out_remove_cache for failures after cache insertion
- send ocfs2_start_trans() failure to out_remove_cache

v2:
- add the missing Fixes tag for the group-add introduction commit
- keep the validation failure path separate so cache removal only happens
  after the buffer has been inserted into main_bm_inode's cache
---
 fs/ocfs2/resize.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/fs/ocfs2/resize.c b/fs/ocfs2/resize.c
index b0733c08ed13..5c6975d90ad6 100644
--- a/fs/ocfs2/resize.c
+++ b/fs/ocfs2/resize.c
@@ -504,14 +504,14 @@ int ocfs2_group_add(struct inode *inode, struct ocfs2_new_group_input *input)
 		goto out_unlock;
 	}
 
-	ocfs2_set_new_buffer_uptodate(INODE_CACHE(inode), group_bh);
-
 	ret = ocfs2_verify_group_and_input(main_bm_inode, fe, input, group_bh);
 	if (ret) {
 		mlog_errno(ret);
 		goto out_free_group_bh;
 	}
 
+	ocfs2_set_new_buffer_uptodate(INODE_CACHE(main_bm_inode), group_bh);
+
 	trace_ocfs2_group_add((unsigned long long)input->group,
 			       input->chain, input->clusters, input->frees);
 
@@ -519,7 +519,7 @@ int ocfs2_group_add(struct inode *inode, struct ocfs2_new_group_input *input)
 	if (IS_ERR(handle)) {
 		mlog_errno(PTR_ERR(handle));
 		ret = -EINVAL;
-		goto out_free_group_bh;
+		goto out_remove_cache;
 	}
 
 	cl_bpc = le16_to_cpu(fe->id2.i_chain.cl_bpc);
@@ -573,9 +573,11 @@ int ocfs2_group_add(struct inode *inode, struct ocfs2_new_group_input *input)
 out_commit:
 	ocfs2_commit_trans(osb, handle);
 
-out_free_group_bh:
+out_remove_cache:
 	if (ret < 0)
-		ocfs2_remove_from_cache(INODE_CACHE(inode), group_bh);
+		ocfs2_remove_from_cache(INODE_CACHE(main_bm_inode), group_bh);
+
+out_free_group_bh:
 	brelse(group_bh);
 
 out_unlock:
-- 
2.43.0