| Message ID | 72945c1bf5ad016642b678764f44a3dcc5cb040b.1724125513.git.fahimitahera@gmail.com (mailing list archive) |
|---|---|
| State | Not Applicable |
| Headers | show |
| Series | Landlock: Add abstract UNIX socket connect restriction | expand |
| Context | Check | Description |
|---|---|---|
| netdev/tree_selection | success | Not a local patch, async |
On Mon, Aug 19, 2024 at 10:08:55PM -0600, Tahera Fahimi wrote: > A sandboxer can receive the character "a" as input from the environment > variable LL_SCOPE to restrict the abstract UNIX sockets from connecting > to a process outside its scoped domain. > > Example > ======= > Create an abstract unix socket to listen with socat(1): > socat abstract-listen:mysocket - > > Create a sandboxed shell and pass the character "a" to LL_SCOPED: > LL_FS_RO=/ LL_FS_RW=. LL_SCOPED="a" ./sandboxer /bin/bash > > If the sandboxed process tries to connect to the listening socket > with command "socat - abstract-connect:mysocket", the connection > will fail. > > Signed-off-by: Tahera Fahimi <fahimitahera@gmail.com> > --- > v10: > - Minor improvement in code based on v9. > v9: > - Add a restrict approach on input of LL_SCOPED, so it only allows zero > or one "a" to be the input. > v8: > - Adding check_ruleset_scope function to parse the scope environment > variable and update the landlock attribute based on the restriction > provided by the user. > - Adding Mickaël Salaün reviews on version 7. > > v7: > - Adding IPC scoping to the sandbox demo by defining a new "LL_SCOPED" > environment variable. "LL_SCOPED" gets value "a" to restrict abstract > unix sockets. > - Change LANDLOCK_ABI_LAST to 6. > --- > samples/landlock/sandboxer.c | 56 +++++++++++++++++++++++++++++++++--- > 1 file changed, 52 insertions(+), 4 deletions(-) > > diff --git a/samples/landlock/sandboxer.c b/samples/landlock/sandboxer.c > index e8223c3e781a..0564d0a40c67 100644 > --- a/samples/landlock/sandboxer.c > +++ b/samples/landlock/sandboxer.c > @@ -14,6 +14,7 @@ > #include <fcntl.h> > #include <linux/landlock.h> > #include <linux/prctl.h> > +#include <linux/socket.h> > #include <stddef.h> > #include <stdio.h> > #include <stdlib.h> > @@ -22,6 +23,7 @@ > #include <sys/stat.h> > #include <sys/syscall.h> > #include <unistd.h> > +#include <stdbool.h> > > #ifndef landlock_create_ruleset > static inline int > @@ -55,6 +57,7 @@ static inline int landlock_restrict_self(const int ruleset_fd, > #define ENV_FS_RW_NAME "LL_FS_RW" > #define ENV_TCP_BIND_NAME "LL_TCP_BIND" > #define ENV_TCP_CONNECT_NAME "LL_TCP_CONNECT" > +#define ENV_SCOPED_NAME "LL_SCOPED" > #define ENV_DELIMITER ":" > > static int parse_path(char *env_path, const char ***const path_list) > @@ -184,6 +187,40 @@ static int populate_ruleset_net(const char *const env_var, const int ruleset_fd, > return ret; > } > > +static bool check_ruleset_scope(const char *const env_var, > + struct landlock_ruleset_attr *ruleset_attr) > +{ > + bool abstract_scoping = false; > + bool ret = true; > + char *env_type_scope, *env_type_scope_next, *ipc_scoping_name; > + > + ruleset_attr->scoped &= ~LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET; This is bug prone because it removes the scope flags but doesn't store the initial state. It would be better to use the abstract_scoping variable to unset the related flag at the end of this function. > + env_type_scope = getenv(env_var); > + /* scoping is not supported by the user */ > + if (!env_type_scope || strcmp("", env_type_scope) == 0) > + return true; > + > + env_type_scope = strdup(env_type_scope); > + unsetenv(env_var); > + env_type_scope_next = env_type_scope; > + while ((ipc_scoping_name = > + strsep(&env_type_scope_next, ENV_DELIMITER))) { > + if (strcmp("a", ipc_scoping_name) == 0 && !abstract_scoping) { > + abstract_scoping = true; > + ruleset_attr->scoped |= > + LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET; > + } else { > + fprintf(stderr, "Unsupported scoping \"%s\"\n", > + ipc_scoping_name); > + ret = false; > + goto out_free_name; > + } > + } > +out_free_name: > + free(env_type_scope); > + return ret; > +} > + > /* clang-format off */ > > #define ACCESS_FS_ROUGHLY_READ ( \ > @@ -208,7 +245,7 @@ static int populate_ruleset_net(const char *const env_var, const int ruleset_fd, > > /* clang-format on */ > > -#define LANDLOCK_ABI_LAST 5 > +#define LANDLOCK_ABI_LAST 6 > > int main(const int argc, char *const argv[], char *const *const envp) > { > @@ -223,14 +260,15 @@ int main(const int argc, char *const argv[], char *const *const envp) > .handled_access_fs = access_fs_rw, > .handled_access_net = LANDLOCK_ACCESS_NET_BIND_TCP | > LANDLOCK_ACCESS_NET_CONNECT_TCP, > + .scoped = LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET, > }; > > if (argc < 2) { > fprintf(stderr, > - "usage: %s=\"...\" %s=\"...\" %s=\"...\" %s=\"...\"%s " > + "usage: %s=\"...\" %s=\"...\" %s=\"...\" %s=\"...\" %s=\"...\" %s " > "<cmd> [args]...\n\n", > ENV_FS_RO_NAME, ENV_FS_RW_NAME, ENV_TCP_BIND_NAME, > - ENV_TCP_CONNECT_NAME, argv[0]); > + ENV_TCP_CONNECT_NAME, ENV_SCOPED_NAME, argv[0]); > fprintf(stderr, > "Execute a command in a restricted environment.\n\n"); > fprintf(stderr, > @@ -251,15 +289,18 @@ int main(const int argc, char *const argv[], char *const *const envp) > fprintf(stderr, > "* %s: list of ports allowed to connect (client).\n", > ENV_TCP_CONNECT_NAME); > + fprintf(stderr, "* %s: list of restrictions on IPCs.\n", > + ENV_SCOPED_NAME); > fprintf(stderr, > "\nexample:\n" > "%s=\"${PATH}:/lib:/usr:/proc:/etc:/dev/urandom\" " > "%s=\"/dev/null:/dev/full:/dev/zero:/dev/pts:/tmp\" " > "%s=\"9418\" " > "%s=\"80:443\" " > + "%s=\"a\" " > "%s bash -i\n\n", > ENV_FS_RO_NAME, ENV_FS_RW_NAME, ENV_TCP_BIND_NAME, > - ENV_TCP_CONNECT_NAME, argv[0]); > + ENV_TCP_CONNECT_NAME, ENV_SCOPED_NAME, argv[0]); > fprintf(stderr, > "This sandboxer can use Landlock features " > "up to ABI version %d.\n", > @@ -327,6 +368,10 @@ int main(const int argc, char *const argv[], char *const *const envp) > /* Removes LANDLOCK_ACCESS_FS_IOCTL_DEV for ABI < 5 */ > ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_IOCTL_DEV; > > + __attribute__((fallthrough)); > + case 5: > + /* Removes LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET for ABI < 6 */ > + ruleset_attr.scoped &= ~LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET; > fprintf(stderr, > "Hint: You should update the running kernel " > "to leverage Landlock features " > @@ -358,6 +403,9 @@ int main(const int argc, char *const argv[], char *const *const envp) > ~LANDLOCK_ACCESS_NET_CONNECT_TCP; > } > > + if (abi >= 6 && !check_ruleset_scope(ENV_SCOPED_NAME, &ruleset_attr)) Instead of explicitly re-checking the ABI, check_ruleset_scope() should check ruleset_attr.scoped & LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET > + return 1; > + > ruleset_fd = > landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0); > if (ruleset_fd < 0) { > -- > 2.34.1 > >
diff --git a/samples/landlock/sandboxer.c b/samples/landlock/sandboxer.c index e8223c3e781a..0564d0a40c67 100644 --- a/samples/landlock/sandboxer.c +++ b/samples/landlock/sandboxer.c @@ -14,6 +14,7 @@ #include <fcntl.h> #include <linux/landlock.h> #include <linux/prctl.h> +#include <linux/socket.h> #include <stddef.h> #include <stdio.h> #include <stdlib.h> @@ -22,6 +23,7 @@ #include <sys/stat.h> #include <sys/syscall.h> #include <unistd.h> +#include <stdbool.h> #ifndef landlock_create_ruleset static inline int @@ -55,6 +57,7 @@ static inline int landlock_restrict_self(const int ruleset_fd, #define ENV_FS_RW_NAME "LL_FS_RW" #define ENV_TCP_BIND_NAME "LL_TCP_BIND" #define ENV_TCP_CONNECT_NAME "LL_TCP_CONNECT" +#define ENV_SCOPED_NAME "LL_SCOPED" #define ENV_DELIMITER ":" static int parse_path(char *env_path, const char ***const path_list) @@ -184,6 +187,40 @@ static int populate_ruleset_net(const char *const env_var, const int ruleset_fd, return ret; } +static bool check_ruleset_scope(const char *const env_var, + struct landlock_ruleset_attr *ruleset_attr) +{ + bool abstract_scoping = false; + bool ret = true; + char *env_type_scope, *env_type_scope_next, *ipc_scoping_name; + + ruleset_attr->scoped &= ~LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET; + env_type_scope = getenv(env_var); + /* scoping is not supported by the user */ + if (!env_type_scope || strcmp("", env_type_scope) == 0) + return true; + + env_type_scope = strdup(env_type_scope); + unsetenv(env_var); + env_type_scope_next = env_type_scope; + while ((ipc_scoping_name = + strsep(&env_type_scope_next, ENV_DELIMITER))) { + if (strcmp("a", ipc_scoping_name) == 0 && !abstract_scoping) { + abstract_scoping = true; + ruleset_attr->scoped |= + LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET; + } else { + fprintf(stderr, "Unsupported scoping \"%s\"\n", + ipc_scoping_name); + ret = false; + goto out_free_name; + } + } +out_free_name: + free(env_type_scope); + return ret; +} + /* clang-format off */ #define ACCESS_FS_ROUGHLY_READ ( \ @@ -208,7 +245,7 @@ static int populate_ruleset_net(const char *const env_var, const int ruleset_fd, /* clang-format on */ -#define LANDLOCK_ABI_LAST 5 +#define LANDLOCK_ABI_LAST 6 int main(const int argc, char *const argv[], char *const *const envp) { @@ -223,14 +260,15 @@ int main(const int argc, char *const argv[], char *const *const envp) .handled_access_fs = access_fs_rw, .handled_access_net = LANDLOCK_ACCESS_NET_BIND_TCP | LANDLOCK_ACCESS_NET_CONNECT_TCP, + .scoped = LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET, }; if (argc < 2) { fprintf(stderr, - "usage: %s=\"...\" %s=\"...\" %s=\"...\" %s=\"...\"%s " + "usage: %s=\"...\" %s=\"...\" %s=\"...\" %s=\"...\" %s=\"...\" %s " "<cmd> [args]...\n\n", ENV_FS_RO_NAME, ENV_FS_RW_NAME, ENV_TCP_BIND_NAME, - ENV_TCP_CONNECT_NAME, argv[0]); + ENV_TCP_CONNECT_NAME, ENV_SCOPED_NAME, argv[0]); fprintf(stderr, "Execute a command in a restricted environment.\n\n"); fprintf(stderr, @@ -251,15 +289,18 @@ int main(const int argc, char *const argv[], char *const *const envp) fprintf(stderr, "* %s: list of ports allowed to connect (client).\n", ENV_TCP_CONNECT_NAME); + fprintf(stderr, "* %s: list of restrictions on IPCs.\n", + ENV_SCOPED_NAME); fprintf(stderr, "\nexample:\n" "%s=\"${PATH}:/lib:/usr:/proc:/etc:/dev/urandom\" " "%s=\"/dev/null:/dev/full:/dev/zero:/dev/pts:/tmp\" " "%s=\"9418\" " "%s=\"80:443\" " + "%s=\"a\" " "%s bash -i\n\n", ENV_FS_RO_NAME, ENV_FS_RW_NAME, ENV_TCP_BIND_NAME, - ENV_TCP_CONNECT_NAME, argv[0]); + ENV_TCP_CONNECT_NAME, ENV_SCOPED_NAME, argv[0]); fprintf(stderr, "This sandboxer can use Landlock features " "up to ABI version %d.\n", @@ -327,6 +368,10 @@ int main(const int argc, char *const argv[], char *const *const envp) /* Removes LANDLOCK_ACCESS_FS_IOCTL_DEV for ABI < 5 */ ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_IOCTL_DEV; + __attribute__((fallthrough)); + case 5: + /* Removes LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET for ABI < 6 */ + ruleset_attr.scoped &= ~LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET; fprintf(stderr, "Hint: You should update the running kernel " "to leverage Landlock features " @@ -358,6 +403,9 @@ int main(const int argc, char *const argv[], char *const *const envp) ~LANDLOCK_ACCESS_NET_CONNECT_TCP; } + if (abi >= 6 && !check_ruleset_scope(ENV_SCOPED_NAME, &ruleset_attr)) + return 1; + ruleset_fd = landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0); if (ruleset_fd < 0) {
A sandboxer can receive the character "a" as input from the environment variable LL_SCOPE to restrict the abstract UNIX sockets from connecting to a process outside its scoped domain. Example ======= Create an abstract unix socket to listen with socat(1): socat abstract-listen:mysocket - Create a sandboxed shell and pass the character "a" to LL_SCOPED: LL_FS_RO=/ LL_FS_RW=. LL_SCOPED="a" ./sandboxer /bin/bash If the sandboxed process tries to connect to the listening socket with command "socat - abstract-connect:mysocket", the connection will fail. Signed-off-by: Tahera Fahimi <fahimitahera@gmail.com> --- v10: - Minor improvement in code based on v9. v9: - Add a restrict approach on input of LL_SCOPED, so it only allows zero or one "a" to be the input. v8: - Adding check_ruleset_scope function to parse the scope environment variable and update the landlock attribute based on the restriction provided by the user. - Adding Mickaël Salaün reviews on version 7. v7: - Adding IPC scoping to the sandbox demo by defining a new "LL_SCOPED" environment variable. "LL_SCOPED" gets value "a" to restrict abstract unix sockets. - Change LANDLOCK_ABI_LAST to 6. --- samples/landlock/sandboxer.c | 56 +++++++++++++++++++++++++++++++++--- 1 file changed, 52 insertions(+), 4 deletions(-)