In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
smb: client: clear setuid\/setgid bit on write with cifsacl\/modefromsid\/posix extensions<\/p>\n
When a file has the setuid or setgid bit set and is written to, the VFS
\nstrips those bits and issues a setattr with ATTR_KILL_SUID\/ATTR_KILL_SGID
\ntogether with an ATTR_MODE carrying the already-cleared mode.<\/p>\n
Both cifs_setattr_unix() and cifs_setattr_nounix() unconditionally dropped
\nATTR_MODE in that case:<\/p>\n
\t\/* skip mode change if it’s just for clearing setuid\/setgid *\/
\n\tif (attrs->ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID))
\n\t\tattrs->ia_valid &= ~ATTR_MODE;<\/p>\n
This is fine for the default mount, where the mode is only emulated via
\nthe DOS read-only attribute and cannot represent the setuid\/setgid bits
\nanyway. However, with the “cifsacl” or “modefromsid” mount options the
\nmode is stored on the server through an ACL (id_mode_to_cifs_acl()), with
\nthe SMB3.1.1 POSIX extensions the mode is sent to the server directly,
\nand with the SMB1 Unix extensions (cifs_setattr_unix) the mode is sent
\nvia CIFSSMBUnixSetPathInfo(). In all those cases dropping ATTR_MODE means
\nthe cleared mode is never pushed to the server, so the setuid\/setgid bit
\nsurvives the write.<\/p>\n
This is a security issue: on local filesystems the setuid bit is stripped
\nwhen a file is written, but over these cifs.ko mounts the bit persists on
\nthe server, potentially allowing an unexpected privilege escalation on
\nsubsequent execution.<\/p>\n
Fix this in two places:<\/p>\n
1. cifs_setattr_nounix(): only take the “skip mode change” shortcut
\n when the mode is emulated via the DOS read-only attribute (i.e.
\n neither cifsacl\/modefromsid nor the SMB3.1.1 POSIX extensions are
\n in effect), so that the cleared mode is propagated to the server
\n in the ACL \/ POSIX cases.<\/p>\n
2. cifs_setattr_unix(): this function is only called when Unix
\n extensions are in effect, so the mode is always stored on the
\n server. Remove the shortcut entirely so that the cleared mode is
\n always pushed.<\/p>\n","protected":false},"excerpt":{"rendered":"
In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
smb: client: clear setuid\/setgid bit on write with cifsacl\/modefromsid\/posix extensions<\/p>\n
When a file has the setuid or setgid bit s<\/p>\n","protected":false},"template":"","meta":[],"categories":[],"tags":[],"class_list":["post-21560","vuln","type-vuln","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/vuln\/21560","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/vuln"}],"about":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/types\/vuln"}],"wp:attachment":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=21560"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=21560"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=21560"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}