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authorPaolo Bonzini <pbonini@redhat.com>2012-10-11 14:20:23 +0200
committerAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>2012-12-05 21:55:54 +0530
commit9fd2ecdc8cb2dc1a8a7c57b6c9c60bc9947b6a73 (patch)
tree8e35d3c982798e3165c9869ca98c3a99446a0717 /fsdev
parent16c6c80ac3a772b42a87b77dfdf0fdac7c607b0e (diff)
downloadqemu-arm-9fd2ecdc8cb2dc1a8a7c57b6c9c60bc9947b6a73.tar.gz
virtfs-proxy-helper: use setresuid and setresgid
The setfsuid and setfsgid system calls are obscure and they complicate the error checking (that glibc's warn_unused_result "feature" forces us to do). Switch to the standard setresuid and setresgid functions. Signed-off-by: Paolo Bonzini <pbonini@redhat.com Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Diffstat (limited to 'fsdev')
-rw-r--r--fsdev/virtfs-proxy-helper.c93
1 files changed, 64 insertions, 29 deletions
diff --git a/fsdev/virtfs-proxy-helper.c b/fsdev/virtfs-proxy-helper.c
index f9a8270ee9..df2a9392b1 100644
--- a/fsdev/virtfs-proxy-helper.c
+++ b/fsdev/virtfs-proxy-helper.c
@@ -272,31 +272,76 @@ static int send_status(int sockfd, struct iovec *iovec, int status)
/*
* from man 7 capabilities, section
* Effect of User ID Changes on Capabilities:
- * 4. If the file system user ID is changed from 0 to nonzero (see setfsuid(2))
- * then the following capabilities are cleared from the effective set:
- * CAP_CHOWN, CAP_DAC_OVERRIDE, CAP_DAC_READ_SEARCH, CAP_FOWNER, CAP_FSETID,
- * CAP_LINUX_IMMUTABLE (since Linux 2.2.30), CAP_MAC_OVERRIDE, and CAP_MKNOD
- * (since Linux 2.2.30). If the file system UID is changed from nonzero to 0,
- * then any of these capabilities that are enabled in the permitted set
- * are enabled in the effective set.
+ * If the effective user ID is changed from nonzero to 0, then the permitted
+ * set is copied to the effective set. If the effective user ID is changed
+ * from 0 to nonzero, then all capabilities are are cleared from the effective
+ * set.
+ *
+ * The setfsuid/setfsgid man pages warn that changing the effective user ID may
+ * expose the program to unwanted signals, but this is not true anymore: for an
+ * unprivileged (without CAP_KILL) program to send a signal, the real or
+ * effective user ID of the sending process must equal the real or saved user
+ * ID of the target process. Even when dropping privileges, it is enough to
+ * keep the saved UID to a "privileged" value and virtfs-proxy-helper won't
+ * be exposed to signals. So just use setresuid/setresgid.
*/
-static int setfsugid(int uid, int gid)
+static int setugid(int uid, int gid, int *suid, int *sgid)
{
+ int retval;
+
/*
- * We still need DAC_OVERRIDE because we don't change
+ * We still need DAC_OVERRIDE because we don't change
* supplementary group ids, and hence may be subjected DAC rules
*/
cap_value_t cap_list[] = {
CAP_DAC_OVERRIDE,
};
- setfsgid(gid);
- setfsuid(uid);
+ *suid = geteuid();
+ *sgid = getegid();
+
+ if (setresgid(-1, gid, *sgid) == -1) {
+ retval = -errno;
+ goto err_out;
+ }
+
+ if (setresuid(-1, uid, *suid) == -1) {
+ retval = -errno;
+ goto err_sgid;
+ }
if (uid != 0 || gid != 0) {
- return do_cap_set(cap_list, ARRAY_SIZE(cap_list), 0);
+ if (do_cap_set(cap_list, ARRAY_SIZE(cap_list), 0) < 0) {
+ retval = -errno;
+ goto err_suid;
+ }
}
return 0;
+
+err_suid:
+ if (setresuid(-1, *suid, *suid) == -1) {
+ abort();
+ }
+err_sgid:
+ if (setresgid(-1, *sgid, *sgid) == -1) {
+ abort();
+ }
+err_out:
+ return retval;
+}
+
+/*
+ * This is used to reset the ugid back with the saved values
+ * There is nothing much we can do checking error values here.
+ */
+static void resetugid(int suid, int sgid)
+{
+ if (setresgid(-1, sgid, sgid) == -1) {
+ abort();
+ }
+ if (setresuid(-1, suid, suid) == -1) {
+ abort();
+ }
}
/*
@@ -578,18 +623,15 @@ static int do_create_others(int type, struct iovec *iovec)
v9fs_string_init(&path);
v9fs_string_init(&oldpath);
- cur_uid = geteuid();
- cur_gid = getegid();
retval = proxy_unmarshal(iovec, offset, "dd", &uid, &gid);
if (retval < 0) {
return retval;
}
offset += retval;
- retval = setfsugid(uid, gid);
+ retval = setugid(uid, gid, &cur_uid, &cur_gid);
if (retval < 0) {
- retval = -errno;
- goto err_out;
+ goto unmarshal_err_out;
}
switch (type) {
case T_MKNOD:
@@ -619,9 +661,10 @@ static int do_create_others(int type, struct iovec *iovec)
}
err_out:
+ resetugid(cur_uid, cur_gid);
+unmarshal_err_out:
v9fs_string_free(&path);
v9fs_string_free(&oldpath);
- setfsugid(cur_uid, cur_gid);
return retval;
}
@@ -641,24 +684,16 @@ static int do_create(struct iovec *iovec)
if (ret < 0) {
goto unmarshal_err_out;
}
- cur_uid = geteuid();
- cur_gid = getegid();
- ret = setfsugid(uid, gid);
+ ret = setugid(uid, gid, &cur_uid, &cur_gid);
if (ret < 0) {
- /*
- * On failure reset back to the
- * old uid/gid
- */
- ret = -errno;
- goto err_out;
+ goto unmarshal_err_out;
}
ret = open(path.data, flags, mode);
if (ret < 0) {
ret = -errno;
}
-err_out:
- setfsugid(cur_uid, cur_gid);
+ resetugid(cur_uid, cur_gid);
unmarshal_err_out:
v9fs_string_free(&path);
return ret;