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Thu, 24 Sep 2026 11:29:04 +0000 (GMT) Received: from macbookpro.bl1-in.ibm.com (unknown [9.123.4.160]) by smtpav03.fra02v.mail.ibm.com (Postfix) with ESMTP; Thu, 24 Sep 2026 11:29:04 +0000 (GMT) From: Disha Goel To: miklos@szeredi.hu, amir73il@gmail.com Cc: brauner@kernel.org, viro@zeniv.linux.org.uk, jack@suse.cz, shuah@kernel.org, linux-unionfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, Disha Goel , stable@vger.kernel.org Subject: [PATCH 1/2] ovl: fix mount setup failing when override_creds drops CAP_SYS_ADMIN Date: Thu, 24 Sep 2026 16:58:57 +0530 Message-ID: <20260924112858.51392-1-disgoel@linux.ibm.com> X-Mailer: git-send-email 2.45.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Authority-Analysis: v=2.4 cv=G+OJgNk5 c=1 sm=1 tr=0 ts=6ab50985 cx=c_pps a=bLidbwmWQ0KltjZqbj+ezA==:117 a=bLidbwmWQ0KltjZqbj+ezA==:17 a=VdqzKS8jKosA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=V8glGbnc2Ofi9Qvn3v5h:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=l8F_COdeiNbdnb7lkW0A:9 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwOTI0MDA0NiBTYWx0ZWRfX+Xxvkqi+jHkD sTnMTwhReEKR9ZjUad9j1/24ewOlpy6+voDWnlbB7fv8OXE8/E78sYM6TNSMrbeewuVXm+F0wsA P9SrVVLdhJq1XwngKOL7BInf4Q9vzvs3waNwdZGW02V5Q9vIxcV/nYF+rxNP65T0x/1GarGWE01 hieEoFtVUpWfhS5OvVWI2HulDNpqPIQjVPWTzsZlHkyKf2z406vFYWPWVyFwOFwHr55ZSKJ7+ce YZM1jxFjXHm81HhR6EIkCnWg7Lcdy9etdHZY5wmssdX68h7DdCECtXhXrzlo1Ar2I2ARRQ/Qv7S w4ORaq4ZKr+mlYp8JQAoUoAo8hMJQeLphtjoEYIXGgPmdD6gGWvfrhIb3+pbSDwPTUstG0HvBIk ZnnjTS4Hjln/uDuL6+3F/Ks5KE5ahZwinaisAL1BeDCspI6slx7UCzfz+js18uoaWHcBEoEdl2U UY6R++LYlOL+aojhj5w== X-Proofpoint-ORIG-GUID: OyqnHgROl3cA-RcydddRci9G5R2lKxWB X-Proofpoint-GUID: 8dTP5fY38y81V1fHLVpC5WXJUaInBj0V X-Proofpoint-Spam-Info: AW1haW4tMjYwOTI0MDA0NiBTYWx0ZWRfXx+DM1i/56qsd cyWl4B9ZBfHwz5mfSdzoQfxoGTpj3bit4okt1gfUEAv9g/GtfkWhV9Kd7F4+QPiBV0VwsCViDvm pWJHbF0LDo1C8+Q2238HVzs1ljbBra4= X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-09-24_02,2026-09-21_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 adultscore=0 phishscore=0 lowpriorityscore=0 impostorscore=0 bulkscore=0 priorityscore=1501 clxscore=1011 spamscore=0 malwarescore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2609040000 definitions=main-2609240046 When a process drops CAP_SYS_ADMIN and calls fsconfig(FSCONFIG_SET_FLAG, "override_creds"), overlayfs saves those restricted credentials in ofs->creator_cred. ovl_fill_super() then wrapped the entire mount setup in with_ovl_creds(), switching to those restricted credentials for the duration. Mount setup calls clone_private_mount(), which checks CAP_SYS_ADMIN against current credentials. With restricted credentials active, this check fails with -EPERM and the mount fails even though the calling process is fully privileged. Mount setup is a one-time privileged operation and must run under the caller's credentials. with_ovl_creds() belongs only in post-mount I/O paths. Remove it from ovl_fill_super(). Fixes: 539a0879de47 ("ovl: allow to specify override credentials") Cc: stable@vger.kernel.org Signed-off-by: Disha Goel --- fs/overlayfs/super.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c index bd0a3f9039d2..29f9489b8242 100644 --- a/fs/overlayfs/super.c +++ b/fs/overlayfs/super.c @@ -1557,8 +1557,12 @@ int ovl_fill_super(struct super_block *sb, struct fs_context *fc) goto out_err; } - with_ovl_creds(sb) - err = ovl_fill_super_creds(fc, sb); + /* + * Mount setup must run under the caller's credentials, not + * creator_cred: clone_private_mount() requires CAP_SYS_ADMIN, + * which override_creds may have dropped. + */ + err = ovl_fill_super_creds(fc, sb); out_err: if (err) { -- 2.45.1