* [PATCH] erofs-utils: fsck: extract zero-length xattr values
@ 2026-11-04 3:52 Wenyuan Xu
2026-11-04 8:36 ` Gao Xiang
0 siblings, 1 reply; 3+ messages in thread
From: Wenyuan Xu @ 2026-11-04 3:52 UTC (permalink / raw)
To: xiang, linux-erofs; +Cc: sereno.xu
A zero return value from erofs_getxattr() denotes an empty attribute,
but the extraction path treats it as an error.
Accept zero-length values and allocate at least one byte for the value
buffer, avoiding dependence on malloc(0) behavior.
Signed-off-by: Wenyuan Xu <sereno.xu@deepseek.com>
---
fsck/main.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/fsck/main.c b/fsck/main.c
index e54c523..9db5ae9 100644
--- a/fsck/main.c
+++ b/fsck/main.c
@@ -458,14 +458,15 @@ static int erofsfsck_dump_xattrs(struct erofs_inode *inode)
size_t size = 0;
ret = erofs_getxattr(inode, key, NULL, 0);
- if (ret <= 0) {
+ if (ret < 0) {
DBG_BUGON(1);
erofs_err("failed to get xattr value size of `%s` @ nid %llu",
key, inode->nid | 0ULL);
break;
}
size = ret;
- value = malloc(size);
+ /* Empty xattrs are valid */
+ value = malloc(size ? size : 1);
if (!value) {
ret = -ENOMEM;
break;
--
2.43.0
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] erofs-utils: fsck: extract zero-length xattr values
2026-11-04 3:52 [PATCH] erofs-utils: fsck: extract zero-length xattr values Wenyuan Xu
@ 2026-11-04 8:36 ` Gao Xiang
2026-11-04 9:04 ` Wenyuan Xu
0 siblings, 1 reply; 3+ messages in thread
From: Gao Xiang @ 2026-11-04 8:36 UTC (permalink / raw)
To: Wenyuan Xu; +Cc: xiang, linux-erofs
Hi Wenyuan,
On Wed, Nov 04, 2026 at 03:52:08AM +0000, Wenyuan Xu wrote:
> A zero return value from erofs_getxattr() denotes an empty attribute,
> but the extraction path treats it as an error.
>
> Accept zero-length values and allocate at least one byte for the value
> buffer, avoiding dependence on malloc(0) behavior.
>
> Signed-off-by: Wenyuan Xu <sereno.xu@deepseek.com>
According to
https://linux.die.net/man/2/getxattr
Return Value
On success, a positive number is returned indicating the
size of the extended attribute value.
So 0-sized xattrs are not a valid number or here is a mistake.
In principle, filesystems accept 0-size xattrs, and
overlayfs uses it (see ovl_path_check_origin_xattr()).
I think EROFS should support 0-size xattrs, but here
we shouldn't expand to 1.
I applied the following diff (please find if it works or not):
diff --git a/fsck/main.c b/fsck/main.c
index 8e3ae52..1a36ef8 100644
--- a/fsck/main.c
+++ b/fsck/main.c
@@ -458,25 +458,33 @@ static int erofsfsck_dump_xattrs(struct erofs_inode *inode)
size_t size = 0;
ret = erofs_getxattr(inode, key, NULL, 0);
- if (ret <= 0) {
+ if (ret < 0) {
DBG_BUGON(1);
erofs_err("failed to get xattr value size of `%s` @ nid %llu",
key, inode->nid | 0ULL);
break;
}
size = ret;
- value = malloc(size);
- if (!value) {
- ret = -ENOMEM;
- break;
- }
- ret = erofs_getxattr(inode, key, value, size);
- if (ret < 0) {
- erofs_err("failed to get xattr `%s` @ nid %llu, because of `%s`", key,
- inode->nid | 0ULL, erofs_strerror(ret));
- free(value);
- break;
+
+ /* Empty xattrs are allowed */
+ if (!size) {
+ value = NULL;
+ } else {
+ value = malloc(size);
+ if (!value) {
+ ret = -ENOMEM;
+ break;
+ }
+
+ ret = erofs_getxattr(inode, key, value, size);
+ if (ret < 0) {
+ erofs_err("failed to get xattr `%s` @ nid %llu, because of `%s`", key,
+ inode->nid | 0ULL, erofs_strerror(ret));
+ free(value);
+ break;
+ }
}
+
if (fsckcfg.extract_path)
ret = erofs_sys_lsetxattr(fsckcfg.extract_path, key,
value, size);
Thanks,
Gao Xiang
> ---
> fsck/main.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/fsck/main.c b/fsck/main.c
> index e54c523..9db5ae9 100644
> --- a/fsck/main.c
> +++ b/fsck/main.c
> @@ -458,14 +458,15 @@ static int erofsfsck_dump_xattrs(struct erofs_inode *inode)
> size_t size = 0;
>
> ret = erofs_getxattr(inode, key, NULL, 0);
> - if (ret <= 0) {
> + if (ret < 0) {
> DBG_BUGON(1);
> erofs_err("failed to get xattr value size of `%s` @ nid %llu",
> key, inode->nid | 0ULL);
> break;
> }
> size = ret;
> - value = malloc(size);
> + /* Empty xattrs are valid */
> + value = malloc(size ? size : 1);
> if (!value) {
> ret = -ENOMEM;
> break;
> --
> 2.43.0
>
>
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] erofs-utils: fsck: extract zero-length xattr values
2026-11-04 8:36 ` Gao Xiang
@ 2026-11-04 9:04 ` Wenyuan Xu
0 siblings, 0 replies; 3+ messages in thread
From: Wenyuan Xu @ 2026-11-04 9:04 UTC (permalink / raw)
To: xiang, linux-erofs
在 2026/11/4 16:36, Gao Xiang 写道:
> Hi Wenyuan,
>
> On Wed, Nov 04, 2026 at 03:52:08AM +0000, Wenyuan Xu wrote:
>> A zero return value from erofs_getxattr() denotes an empty attribute,
>> but the extraction path treats it as an error.
>>
>> Accept zero-length values and allocate at least one byte for the value
>> buffer, avoiding dependence on malloc(0) behavior.
>>
>> Signed-off-by: Wenyuan Xu <sereno.xu@deepseek.com>
> According to
> https://linux.die.net/man/2/getxattr
>
> Return Value
> On success, a positive number is returned indicating the
> size of the extended attribute value.
>
> So 0-sized xattrs are not a valid number or here is a mistake.
>
> In principle, filesystems accept 0-size xattrs, and
> overlayfs uses it (see ovl_path_check_origin_xattr()).
>
> I think EROFS should support 0-size xattrs, but here
> we shouldn't expand to 1.
>
> I applied the following diff (please find if it works or not):
LGTM and it works for me.
Thanks.
Wenyuan Xu
> diff --git a/fsck/main.c b/fsck/main.c
> index 8e3ae52..1a36ef8 100644
> --- a/fsck/main.c
> +++ b/fsck/main.c
> @@ -458,25 +458,33 @@ static int erofsfsck_dump_xattrs(struct erofs_inode *inode)
> size_t size = 0;
>
> ret = erofs_getxattr(inode, key, NULL, 0);
> - if (ret <= 0) {
> + if (ret < 0) {
> DBG_BUGON(1);
> erofs_err("failed to get xattr value size of `%s` @ nid %llu",
> key, inode->nid | 0ULL);
> break;
> }
> size = ret;
> - value = malloc(size);
> - if (!value) {
> - ret = -ENOMEM;
> - break;
> - }
> - ret = erofs_getxattr(inode, key, value, size);
> - if (ret < 0) {
> - erofs_err("failed to get xattr `%s` @ nid %llu, because of `%s`", key,
> - inode->nid | 0ULL, erofs_strerror(ret));
> - free(value);
> - break;
> +
> + /* Empty xattrs are allowed */
> + if (!size) {
> + value = NULL;
> + } else {
> + value = malloc(size);
> + if (!value) {
> + ret = -ENOMEM;
> + break;
> + }
> +
> + ret = erofs_getxattr(inode, key, value, size);
> + if (ret < 0) {
> + erofs_err("failed to get xattr `%s` @ nid %llu, because of `%s`", key,
> + inode->nid | 0ULL, erofs_strerror(ret));
> + free(value);
> + break;
> + }
> }
> +
> if (fsckcfg.extract_path)
> ret = erofs_sys_lsetxattr(fsckcfg.extract_path, key,
> value, size);
>
> Thanks,
> Gao Xiang
>
>> ---
>> fsck/main.c | 5 +++--
>> 1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/fsck/main.c b/fsck/main.c
>> index e54c523..9db5ae9 100644
>> --- a/fsck/main.c
>> +++ b/fsck/main.c
>> @@ -458,14 +458,15 @@ static int erofsfsck_dump_xattrs(struct erofs_inode *inode)
>> size_t size = 0;
>>
>> ret = erofs_getxattr(inode, key, NULL, 0);
>> - if (ret <= 0) {
>> + if (ret < 0) {
>> DBG_BUGON(1);
>> erofs_err("failed to get xattr value size of `%s` @ nid %llu",
>> key, inode->nid | 0ULL);
>> break;
>> }
>> size = ret;
>> - value = malloc(size);
>> + /* Empty xattrs are valid */
>> + value = malloc(size ? size : 1);
>> if (!value) {
>> ret = -ENOMEM;
>> break;
>> --
>> 2.43.0
>>
>>
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2026-11-04 9:09 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz follow: Atom feed
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2026-11-04 3:52 [PATCH] erofs-utils: fsck: extract zero-length xattr values Wenyuan Xu
2026-11-04 8:36 ` Gao Xiang
2026-11-04 9:04 ` Wenyuan Xu
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