qemu: fix CVE-2021-20263

virtiofs: drop remapped security.capability xattr as needed

(From OE-Core rev: 7ad71de89dd60700cbaad2df1937bc3d743112da)

Signed-off-by: Sakib Sajal <sakib.sajal@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

2 files changed, 215 insertions, 0 deletions

diff --git a/meta/recipes-devtools/qemu/qemu.inc b/meta/recipes-devtools/qemu/qemu.inc
index d120b0822f..486f404668 100644
--- a/meta/recipes-devtools/qemu/qemu.inc
+++ b/meta/recipes-devtools/qemu/qemu.inc
@@ -56,6 +56,7 @@ SRC_URI = "https://download.qemu.org/${BPN}-${PV}.tar.xz \
            file://CVE-2021-20257.patch \
            file://CVE-2021-3392.patch \
            file://CVE-2020-27821.patch \
+           file://CVE-2021-20263.patch \
            "
 UPSTREAM_CHECK_REGEX = "qemu-(?P<pver>\d+(\.\d+)+)\.tar"
 
diff --git a/meta/recipes-devtools/qemu/qemu/CVE-2021-20263.patch b/meta/recipes-devtools/qemu/qemu/CVE-2021-20263.patch
new file mode 100644
index 0000000000..4f9a91f0c6
--- /dev/null
+++ b/meta/recipes-devtools/qemu/qemu/CVE-2021-20263.patch
@@ -0,0 +1,214 @@
+From aaa5f8e00c2e85a893b972f1e243fb14c26b70dc Mon Sep 17 00:00:00 2001
+From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
+Date: Wed, 24 Feb 2021 19:56:25 +0000
+Subject: [PATCH 2/2] virtiofs: drop remapped security.capability xattr as
+ needed
+
+On Linux, the 'security.capability' xattr holds a set of
+capabilities that can change when an executable is run, giving
+a limited form of privilege escalation to those programs that
+the writer of the file deemed worthy.
+
+Any write causes the 'security.capability' xattr to be dropped,
+stopping anyone from gaining privilege by modifying a blessed
+file.
+
+Fuse relies on the daemon to do this dropping, and in turn the
+daemon relies on the host kernel to drop the xattr for it.  However,
+with the addition of -o xattrmap, the xattr that the guest
+stores its capabilities in is now not the same as the one that
+the host kernel automatically clears.
+
+Where the mapping changes 'security.capability', explicitly clear
+the remapped name to preserve the same behaviour.
+
+This bug is assigned CVE-2021-20263.
+
+Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
+Reviewed-by: Vivek Goyal <vgoyal@redhat.com>
+
+Upstream-Status: Backport [e586edcb410543768ef009eaa22a2d9dd4a53846]
+CVE: CVE-2021-20263
+
+Signed-off-by: Sakib Sajal <sakib.sajal@windriver.com>
+---
+ docs/tools/virtiofsd.rst         |  4 ++
+ tools/virtiofsd/passthrough_ll.c | 77 +++++++++++++++++++++++++++++++-
+ 2 files changed, 80 insertions(+), 1 deletion(-)
+
+diff --git a/docs/tools/virtiofsd.rst b/docs/tools/virtiofsd.rst
+index 866b7db3e..00554c75b 100644
+--- a/docs/tools/virtiofsd.rst
++++ b/docs/tools/virtiofsd.rst
+@@ -228,6 +228,10 @@ The 'map' type adds a number of separate rules to add **prepend** as a prefix
+ to the matched **key** (or all attributes if **key** is empty).
+ There may be at most one 'map' rule and it must be the last rule in the set.
+ 
++Note: When the 'security.capability' xattr is remapped, the daemon has to do
++extra work to remove it during many operations, which the host kernel normally
++does itself.
++
+ xattr-mapping Examples
+ ----------------------
+ 
+diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c
+index 03c5e0d13..c9197da86 100644
+--- a/tools/virtiofsd/passthrough_ll.c
++++ b/tools/virtiofsd/passthrough_ll.c
+@@ -160,6 +160,7 @@ struct lo_data {
+     int posix_lock;
+     int xattr;
+     char *xattrmap;
++    char *xattr_security_capability;
+     char *source;
+     char *modcaps;
+     double timeout;
+@@ -226,6 +227,8 @@ static __thread bool cap_loaded = 0;
+ 
+ static struct lo_inode *lo_find(struct lo_data *lo, struct stat *st,
+                                 uint64_t mnt_id);
++static int xattr_map_client(const struct lo_data *lo, const char *client_name,
++                            char **out_name);
+ 
+ static int is_dot_or_dotdot(const char *name)
+ {
+@@ -365,6 +368,37 @@ out:
+     return ret;
+ }
+ 
++/*
++ * The host kernel normally drops security.capability xattr's on
++ * any write, however if we're remapping xattr names we need to drop
++ * whatever the clients security.capability is actually stored as.
++ */
++static int drop_security_capability(const struct lo_data *lo, int fd)
++{
++    if (!lo->xattr_security_capability) {
++        /* We didn't remap the name, let the host kernel do it */
++        return 0;
++    }
++    if (!fremovexattr(fd, lo->xattr_security_capability)) {
++        /* All good */
++        return 0;
++    }
++
++    switch (errno) {
++    case ENODATA:
++        /* Attribute didn't exist, that's fine */
++        return 0;
++
++    case ENOTSUP:
++        /* FS didn't support attribute anyway, also fine */
++        return 0;
++
++    default:
++        /* Hmm other error */
++        return errno;
++    }
++}
++
+ static void lo_map_init(struct lo_map *map)
+ {
+     map->elems = NULL;
+@@ -717,6 +751,11 @@ static void lo_setattr(fuse_req_t req, fuse_ino_t ino, struct stat *attr,
+         uid_t uid = (valid & FUSE_SET_ATTR_UID) ? attr->st_uid : (uid_t)-1;
+         gid_t gid = (valid & FUSE_SET_ATTR_GID) ? attr->st_gid : (gid_t)-1;
+ 
++        saverr = drop_security_capability(lo, ifd);
++        if (saverr) {
++            goto out_err;
++        }
++
+         res = fchownat(ifd, "", uid, gid, AT_EMPTY_PATH | AT_SYMLINK_NOFOLLOW);
+         if (res == -1) {
+             goto out_err;
+@@ -735,6 +774,14 @@ static void lo_setattr(fuse_req_t req, fuse_ino_t ino, struct stat *attr,
+             }
+         }
+ 
++       saverr = drop_security_capability(lo, truncfd);
++        if (saverr) {
++            if (!fi) {
++                close(truncfd);
++            }
++            goto out_err;
++        }
++
+         res = ftruncate(truncfd, attr->st_size);
+         if (!fi) {
+             saverr = errno;
+@@ -1726,6 +1773,13 @@ static int lo_do_open(struct lo_data *lo, struct lo_inode *inode,
+         if (fd < 0) {
+             return -fd;
+         }
++        if (fi->flags & (O_TRUNC)) {
++            int err = drop_security_capability(lo, fd);
++            if (err) {
++                close(fd);
++                return err;
++            }
++        }
+     }
+ 
+     pthread_mutex_lock(&lo->mutex);
+@@ -2114,6 +2168,12 @@ static void lo_write_buf(fuse_req_t req, fuse_ino_t ino,
+              "lo_write_buf(ino=%" PRIu64 ", size=%zd, off=%lu)\n", ino,
+              out_buf.buf[0].size, (unsigned long)off);
+ 
++    res = drop_security_capability(lo_data(req), out_buf.buf[0].fd);
++    if (res) {
++        fuse_reply_err(req, res);
++        return;
++    }
++
+     /*
+      * If kill_priv is set, drop CAP_FSETID which should lead to kernel
+      * clearing setuid/setgid on file.
+@@ -2353,6 +2413,7 @@ static void parse_xattrmap(struct lo_data *lo)
+ {
+     const char *map = lo->xattrmap;
+     const char *tmp;
++    int ret;
+ 
+     lo->xattr_map_nentries = 0;
+     while (*map) {
+@@ -2383,7 +2444,7 @@ static void parse_xattrmap(struct lo_data *lo)
+              * the last entry.
+              */
+             parse_xattrmap_map(lo, map, sep);
+-            return;
++            break;
+         } else {
+             fuse_log(FUSE_LOG_ERR,
+                      "%s: Unexpected type;"
+@@ -2452,6 +2513,19 @@ static void parse_xattrmap(struct lo_data *lo)
+         fuse_log(FUSE_LOG_ERR, "Empty xattr map\n");
+         exit(1);
+     }
++
++    ret = xattr_map_client(lo, "security.capability",
++                           &lo->xattr_security_capability);
++    if (ret) {
++        fuse_log(FUSE_LOG_ERR, "Failed to map security.capability: %s\n",
++                strerror(ret));
++        exit(1);
++    }
++    if (!strcmp(lo->xattr_security_capability, "security.capability")) {
++        /* 1-1 mapping, don't need to do anything */
++        free(lo->xattr_security_capability);
++        lo->xattr_security_capability = NULL;
++    }
+ }
+ 
+ /*
+@@ -3480,6 +3554,7 @@ static void fuse_lo_data_cleanup(struct lo_data *lo)
+ 
+     free(lo->xattrmap);
+     free_xattrmap(lo);
++    free(lo->xattr_security_capability);
+     free(lo->source);
+ }
+ 
+-- 
+2.29.2
+