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Subject: [PATCH 1/2] ext4: dont return EINVAL from GETFSUUID when reporting
 UUID length
From:   "Darrick J. Wong" <djwong@kernel.org>
To:     djwong@kernel.org, tytso@mit.edu
Cc:     catherine.hoang@oracle.com, linux-ext4@vger.kernel.org
Date:   Thu, 10 Nov 2022 12:16:29 -0800
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From: Darrick J. Wong <djwong@kernel.org>

If userspace calls this ioctl with fsu_length (the length of the
fsuuid.fsu_uuid array) set to zero, ext4 copies the desired uuid length
out to userspace.  The kernel call returned a result from a valid input,
so the return value here should be zero, not EINVAL.

While we're at it, fix the copy_to_user call to make it clear that we're
only copying out fsu_len.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
---
 fs/ext4/ioctl.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)


diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
index 95dfea28bf4e..5f91f3ad3e50 100644
--- a/fs/ext4/ioctl.c
+++ b/fs/ext4/ioctl.c
@@ -1153,9 +1153,10 @@ static int ext4_ioctl_getuuid(struct ext4_sb_info *sbi,
 
 	if (fsuuid.fsu_len == 0) {
 		fsuuid.fsu_len = UUID_SIZE;
-		if (copy_to_user(ufsuuid, &fsuuid, sizeof(fsuuid.fsu_len)))
+		if (copy_to_user(&ufsuuid->fsu_len, &fsuuid.fsu_len,
+					sizeof(fsuuid.fsu_len)))
 			return -EFAULT;
-		return -EINVAL;
+		return 0;
 	}
 
 	if (fsuuid.fsu_len != UUID_SIZE || fsuuid.fsu_flags != 0)