Re: [PATCH bpf-next v4 03/20] lsm: Refactor return value of LSM hook inode_getsecurity

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On 7/12/2024 9:31 PM, Simon Horman wrote:
On Thu, Jul 11, 2024 at 07:18:51PM +0800, Xu Kuohai wrote:
From: Xu Kuohai <xukuohai@xxxxxxxxxx>

To be consistent with most LSM hooks, convert the return value of
hook inode_getsecurity to 0 or a negative error code.

Before:
- Hook inode_getsecurity returns size of buffer on success or a
   negative error code on failure.

After:
- Hook inode_getsecurity returns 0 on success or a negative error
   code on failure. An output parameter @len is introduced to hold
   the buffer size on success.

Signed-off-by: Xu Kuohai <xukuohai@xxxxxxxxxx>
---
  fs/xattr.c                    | 19 ++++++++++---------
  include/linux/lsm_hook_defs.h |  3 ++-
  include/linux/security.h      | 12 ++++++------
  security/commoncap.c          |  9 ++++++---
  security/security.c           | 11 ++++++-----
  security/selinux/hooks.c      | 16 ++++++----------
  security/smack/smack_lsm.c    | 14 +++++++-------
  7 files changed, 43 insertions(+), 41 deletions(-)

diff --git a/fs/xattr.c b/fs/xattr.c
index f8b643f91a98..f4e3bedf7272 100644
--- a/fs/xattr.c
+++ b/fs/xattr.c
@@ -339,27 +339,28 @@ xattr_getsecurity(struct mnt_idmap *idmap, struct inode *inode,
  		  const char *name, void *value, size_t size)
  {
  	void *buffer = NULL;
-	ssize_t len;
+	int error;
+	u32 len;
if (!value || !size) {
-		len = security_inode_getsecurity(idmap, inode, name,
-						 &buffer, false);
+		error = security_inode_getsecurity(idmap, inode, name,
+						   false, &buffer, &len);
  		goto out_noalloc;
  	}
- len = security_inode_getsecurity(idmap, inode, name, &buffer,
-					 true);
-	if (len < 0)
-		return len;
+	error = security_inode_getsecurity(idmap, inode, name, true,
+					   &buffer, &len);
+	if (error)
+		return error;
  	if (size < len) {
-		len = -ERANGE;
+		error = -ERANGE;
  		goto out;
  	}
  	memcpy(value, buffer, len);
  out:
  	kfree(buffer);
  out_noalloc:
-	return len;
+	return error < 0 ? error : len;

Hi Xu Kuohai,

len is an unsigned 32-bit entity, but the return type of this function
is an unsigned value (ssize_t). So in theory, if len is very large,
a negative error value error will be returned.

  }

Similarly for the handling of nattr in lsm_get_self_attr in
lsm_syscalls.c in a subsequent patch.

Flagged by Smatch.

...



OK, indeed there is no standardization that says ssize_t must be wider than u32.
I'll look into adding overflow checks. Thanks.





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