diff options
| -rw-r--r-- | fsdev/virtfs-proxy-helper.c | 93 |
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; |