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file: extend exec acl checks to commands with arguments

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When the initial exec permission check on the executable path fails,
concatenate the command line with spaces and use the resulting string
as lookup path for a second exec permission check.

This allows for exec acls similar to this example:

    "file": {
        "/usr/bin/program --flag --option=1 arg *": [ "exec" ]
    }

The example above would allow executing `/usr/bin/program` with the
arguments `--flag`, `--option=1` and `arg` in exactly this order,
followed by any number of optional arguments as denoted by the
asterisk.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>
This commit is contained in:
Jo-Philipp Wich 2019-12-10 16:49:55 +01:00
parent 77ad0de092
commit aaa08366e6
1 changed files with 28 additions and 2 deletions
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30
file.c
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@ -43,6 +43,9 @@
/* limit of regular files and command output data */
#define RPC_FILE_MAX_SIZE (4096 * 64)
/* limit of command line length for exec acl checks */
#define RPC_CMDLINE_MAX_SIZE (1024)
#define ustream_for_each_read_buffer(stream, ptr, len) \
for (ptr = ustream_get_read_buf(stream, &len); \
ptr != NULL && len > 0; \
@ -71,6 +74,7 @@ struct rpc_file_exec_context {
static struct blob_buf buf;
static char *canonpath;
static char cmdstr[RPC_CMDLINE_MAX_SIZE];
enum {
RPC_F_R_PATH,
@ -801,7 +805,7 @@ rpc_file_exec_run(const char *cmd, const struct blob_attr *sid,
struct blob_attr *cur;
uint8_t arglen;
char *executable, **args, **tmp;
char *executable, **args, **tmp, *p;
struct rpc_file_exec_context *c;
@ -816,7 +820,29 @@ rpc_file_exec_run(const char *cmd, const struct blob_attr *sid,
return UBUS_STATUS_UNKNOWN_ERROR;
if (!rpc_file_access(sid, executable, "exec"))
return UBUS_STATUS_PERMISSION_DENIED;
{
if (arg == NULL || strlen(executable) >= sizeof(cmdstr))
return UBUS_STATUS_PERMISSION_DENIED;
arglen = 0;
p = cmdstr + sprintf(cmdstr, "%s", executable);
blobmsg_for_each_attr(cur, arg, rem)
{
if (blobmsg_type(cur) != BLOBMSG_TYPE_STRING)
continue;
if (arglen == 255 ||
p + blobmsg_data_len(cur) >= cmdstr + sizeof(cmdstr))
break;
p += sprintf(p, " %s", blobmsg_get_string(cur));
arglen++;
}
if (!rpc_file_access(sid, cmdstr, "exec"))
return UBUS_STATUS_PERMISSION_DENIED;
}
c = malloc(sizeof(*c));