Re: [libvirt] [PATCH 2/3] Introduce readonly without explicit deny-write

[Sorry, the Ubuntu package suggests this came from Cèdric, although I can't quite find this patch on the mailing list. Those patches which I did see from Cèdric did not have a Signed-off-by, so I didn't add one for him.]

From: Cèdric Bosdonnat <cbosdonnat(a)suse.com&gt; Upstream changed get_files to unconditionally be "rw" to allow audit files to be written. Still under discussion but the proposed approach is to have a way of saying readonly but do not implicitely create a write deny rule. --- Changelog: do not overwrite const memory, that leads to segv (serge) --- src/security/virt-aa-helper.c | 23 +++++++++++++++++++---- 1 file changed, 19 insertions(+), 4 deletions(-) diff --git a/src/security/virt-aa-helper.c b/src/security/virt-aa -helper.c index b466626..34d08c8 100644 --- a/src/security/virt-aa-helper.c +++ b/src/security/virt-aa-helper.c @@ -785,12 +785,19 @@ get_definition(vahControl * ctl, const char *xmlStr) return rc; } +/* + * The permissions allowed are apparmor valid permissions and 'R'. 'R' stands + * for read with no explicit deny rule. + */ static int -vah_add_path(virBufferPtr buf, const char *path, const char *perms, bool recursive) +vah_add_path(virBufferPtr buf, const char *path, const char *inperms, bool recursive) { char *tmp = NULL; int rc = -1; bool readonly = true; + bool explicit_deny_rule = true; + char *perms = strdupa(inperms); + char *sub = NULL; if (path == NULL) return rc; @@ -815,8 +822,16 @@ vah_add_path(virBufferPtr buf, const char *path, const char *perms, bool recursi return rc; } - if (strchr(perms, 'w') != NULL) + if (strchr(perms, 'w') != NULL) { readonly = false; + explicit_deny_rule = false; + } + + if ((sub = strchr(perms, 'R')) != NULL) { + /* Don't write the invalid 'R' permission, replace with 'r' */ + sub[0] = 'r'; + explicit_deny_rule = false; + } rc = valid_path(tmp, readonly); if (rc != 0) { @@ -831,7 +846,7 @@ vah_add_path(virBufferPtr buf, const char *path, const char *perms, bool recursi tmp[strlen(tmp) - 1] = '\0'; virBufferAsprintf(buf, " \"%s%s\" %s,\n", tmp, recursive ? "/**" : "", perms); - if (readonly) { + if (explicit_deny_rule) { virBufferAddLit(buf, " # don't audit writes to readonly files\n"); virBufferAsprintf(buf, " deny \"%s%s\" w,\n", tmp, recursive ? "/**" : ""); } @@ -1130,7 +1145,7 @@ get_files(vahControl * ctl) /* We don't need to add deny rw rules for readonly mounts, * this can only lead to troubles when mounting / readonly. */ - if (vah_add_path(&buf, fs->src, "rw", true) != 0) + if (vah_add_path(&buf, fs->src, fs->readonly ? "R" : "rw", true) != 0) goto cleanup; } }