diff mbox series

[pseudo,6/7] exec*: Replace bash workaround to avoid memory corruption

Message ID 20260701131336.3578279-6-richard.purdie@linuxfoundation.org
State New
Headers show
Series [pseudo,1/7] pseudo.h: Avoid accessing unallocated memory | expand

Commit Message

Richard Purdie July 1, 2026, 1:13 p.m. UTC 
Bash intercepts getenv/setenv/unsetenv and does magic with it internally.

The data pointed to by environ may not be allocated by glibc but by bash
and the glibc env functions have their own memory handling outside of malloc.
Unfortuantely bash doesn't keep environ and the result of setenv/getenv/unsetenv
in sync either. This means the current workaround badly corrupts memory and it
is just luck we're not breaking more often than the occasional opkg-build segfaults
we've been seeing.

Fixing this is tricky, the best we can probably do is to read through environ and
create our own copy of the it, modifying it how we need to keep the pseudo variables
correct.

We do already have a function which can copyn and modify the environment, we can
therefore swap some setupenv calls for setupenvp and switch out environ around
the exec calls.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
---
 ports/common/guts/execv.c  | 19 ++++++++++++++-----
 ports/common/guts/execvp.c | 15 ++++++++++++---
 ports/unix/guts/popen.c    | 16 +++++++++++++---
 ports/unix/guts/system.c   | 16 +++++++++++++---
 pseudo_client.h            |  3 ---
 pseudo_util.c              | 12 +++---------
 pseudo_wrappers.c          |  6 ------
 7 files changed, 55 insertions(+), 32 deletions(-)

Comments

Gaël PORTAY July 2, 2026, 5:54 a.m. UTC | #1 
Hello Richard,

On Wed Jul 1, 2026 at 3:13 PM CEST, Richard Purdie via lists.yoctoproject.org wrote:
> Bash intercepts getenv/setenv/unsetenv and does magic with it internally.
>
> The data pointed to by environ may not be allocated by glibc but by bash
> and the glibc env functions have their own memory handling outside of malloc.
> Unfortuantely bash doesn't keep environ and the result of setenv/getenv/unsetenv
> in sync either. This means the current workaround badly corrupts memory and it
> is just luck we're not breaking more often than the occasional opkg-build segfaults
> we've been seeing.
>
> Fixing this is tricky, the best we can probably do is to read through environ and
> create our own copy of the it, modifying it how we need to keep the pseudo variables
> correct.
>
> We do already have a function which can copyn and modify the environment, we can

s,copyn,copy,

> therefore swap some setupenv calls for setupenvp and switch out environ around
> the exec calls.
>
> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
> ---
>  ports/common/guts/execv.c  | 19 ++++++++++++++-----
>  ports/common/guts/execvp.c | 15 ++++++++++++---
>  ports/unix/guts/popen.c    | 16 +++++++++++++---
>  ports/unix/guts/system.c   | 16 +++++++++++++---

Don't you need to make these changes to execve(), and posix_spawn{,p}()?
i.e. in files:
 - ports/common/guts/posix_spawnp.c
 - ports/common/guts/posix_spawn.c
 - ports/common/guts/execve.c

Regards,
Gaël
Richard Purdie July 2, 2026, 6:23 a.m. UTC | #2 
Hi Gaël,

On Thu, 2026-07-02 at 07:54 +0200, Gaël PORTAY via lists.yoctoproject.org wrote:
> On Wed Jul 1, 2026 at 3:13 PM CEST, Richard Purdie via lists.yoctoproject.org wrote:
> > Bash intercepts getenv/setenv/unsetenv and does magic with it internally.
> > 
> > The data pointed to by environ may not be allocated by glibc but by bash
> > and the glibc env functions have their own memory handling outside of malloc.
> > Unfortuantely bash doesn't keep environ and the result of setenv/getenv/unsetenv
> > in sync either. This means the current workaround badly corrupts memory and it
> > is just luck we're not breaking more often than the occasional opkg-build segfaults
> > we've been seeing.
> > 
> > Fixing this is tricky, the best we can probably do is to read through environ and
> > create our own copy of the it, modifying it how we need to keep the pseudo variables
> > correct.
> > 
> > We do already have a function which can copyn and modify the environment, we can
> 
> s,copyn,copy,

I'll tweak, thanks.

> > therefore swap some setupenv calls for setupenvp and switch out environ around
> > the exec calls.
> > 
> > Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
> > ---
> >  ports/common/guts/execv.c  | 19 ++++++++++++++-----
> >  ports/common/guts/execvp.c | 15 ++++++++++++---
> >  ports/unix/guts/popen.c    | 16 +++++++++++++---
> >  ports/unix/guts/system.c   | 16 +++++++++++++---
> 
> Don't you need to make these changes to execve(), and posix_spawn{,p}()?
> i.e. in files:
>  - ports/common/guts/posix_spawnp.c
>  - ports/common/guts/posix_spawn.c
>  - ports/common/guts/execve.c

Those already have a environment being passed in and so they already
use setupenvp and we don't need to change that. We only need to change
the places setupenv is being used.

There are still some setupenv calls left and in theory we probably
don't need many of them but they're harmless as long as we use bash's
setenv so I just left them.

Cheers,

Richard
diff mbox series

Patch

diff --git a/ports/common/guts/execv.c b/ports/common/guts/execv.c
index 7819911..eb328ed 100644
--- a/ports/common/guts/execv.c
+++ b/ports/common/guts/execv.c
@@ -8,6 +8,8 @@ 
  * wrap_execv(const char *file, char *const *argv) {
  *	int rc = -1;
  */
+	char **new_environ, **orig_environ;
+
 	/* note:  we don't canonicalize this, because we are intentionally
 	 * NOT redirecting execs into the chroot environment.  If you try
 	 * to execute /bin/sh, you get the actual /bin/sh, not
@@ -19,17 +21,24 @@ 
                 pseudo_client_op(OP_EXEC, PSA_EXEC, -1, -1, path_guess, 0);
 	}
 
-	pseudo_setupenv();
-	if (pseudo_has_unload(NULL)) {
-		/* and here we attach */
-		pseudo_dropenv();
-	}
+	/* Due to bash intercepting setenv/getenv/unsetenv and changing environ
+	   internally itself at will, we create our own environ copy at process
+	   creation based on it to ensure it is correct */
+	orig_environ = environ;
+	new_environ = pseudo_setupenvp(environ);
+	if (pseudo_has_unload(new_environ))
+		new_environ = pseudo_dropenvp(new_environ);
+	environ = new_environ;
+
 	/* if exec() fails, we may end up taking signals unexpectedly...
 	 * not much we can do about that.
 	 */
 	sigprocmask(SIG_SETMASK, &pseudo_saved_sigmask, NULL);
 	rc = real_execv(file, argv);
 
+	environ = orig_environ;
+	free(new_environ);
+
 /*	return rc;
  * }
  */
diff --git a/ports/common/guts/execvp.c b/ports/common/guts/execvp.c
index acc9fdc..177e4ee 100644
--- a/ports/common/guts/execvp.c
+++ b/ports/common/guts/execvp.c
@@ -8,6 +8,7 @@ 
  * wrap_execvp(const char *file, char *const *argv) {
  *	int rc = -1;
  */
+	char **new_environ, **orig_environ;
 
 	/* note:  we don't canonicalize this, because we are intentionally
 	 * NOT redirecting execs into the chroot environment.  If you try
@@ -20,9 +21,14 @@ 
                 pseudo_client_op(OP_EXEC, PSA_EXEC, -1, -1, path_guess, 0);
         }
 
-	pseudo_setupenv();
-	if (pseudo_has_unload(NULL))
-		pseudo_dropenv();
+	/* Due to bash intercepting setenv/getenv/unsetenv and changing environ 
+	   internally itself at will, we create our own environ copy at process
+	   creation based on it to ensure it is correct */
+	orig_environ = environ;
+	new_environ = pseudo_setupenvp(environ);
+	if (pseudo_has_unload(new_environ))
+		new_environ = pseudo_dropenvp(new_environ);
+	environ = new_environ;
 
 	/* if exec() fails, we may end up taking signals unexpectedly...
 	 * not much we can do about that.
@@ -30,6 +36,9 @@ 
 	sigprocmask(SIG_SETMASK, &pseudo_saved_sigmask, NULL);
 	rc = real_execvp(file, argv);
 
+	environ = orig_environ;
+	free(new_environ);
+
 /*	return rc;
  * }
  */
diff --git a/ports/unix/guts/popen.c b/ports/unix/guts/popen.c
index d19ec7e..1d48d04 100644
--- a/ports/unix/guts/popen.c
+++ b/ports/unix/guts/popen.c
@@ -7,15 +7,25 @@ 
  * FILE *popen(const char *command, const char *mode)
  *	FILE *rc = NULL;
  */
+	char **new_environ, **orig_environ;
+
 	/* on at least some systems, popen() calls fork and exec
 	 * in ways that avoid our usual enforcement of the environment.
 	 */
-	pseudo_setupenv();
-	if (pseudo_has_unload(NULL))
-		pseudo_dropenv();
+	/* Due to bash intercepting setenv/getenv/unsetenv and changing environ
+	   internally itself at will, we create our own environ copy at process
+	   creation based on it to ensure it is correct */
+	orig_environ = environ;
+	new_environ = pseudo_setupenvp(environ);
+	if (pseudo_has_unload(new_environ))
+		new_environ = pseudo_dropenvp(new_environ);
+        environ = new_environ;
 
 	rc = real_popen(command, mode);
 
+	environ = orig_environ;
+	free(new_environ);
+
 /*	return rc;
  * }
  */
diff --git a/ports/unix/guts/system.c b/ports/unix/guts/system.c
index 1214314..4b374ec 100644
--- a/ports/unix/guts/system.c
+++ b/ports/unix/guts/system.c
@@ -7,15 +7,25 @@ 
  * int system(const char *command)
  *	int rc = -1;
  */
+	char **new_environ, **orig_environ;
+
 	if (!command)
 		return 1;
 
-	pseudo_setupenv();
-	if (pseudo_has_unload(NULL))
-		pseudo_dropenv();
+	/* Due to bash intercepting setenv/getenv/unsetenv and changing environ
+	   internally itself at will, we create our own environ copy at process
+	   creation based on it to ensure it is correct */
+	orig_environ = environ;
+	new_environ = pseudo_setupenvp(environ);
+	if (pseudo_has_unload(new_environ))
+		new_environ = pseudo_dropenvp(new_environ);
+	environ = new_environ;
 
 	rc = real_system(command);
 
+	environ = orig_environ;
+	free(new_environ);
+
 /*	return rc;
  * }
  */
diff --git a/pseudo_client.h b/pseudo_client.h
index a013f88..43bbc0a 100644
--- a/pseudo_client.h
+++ b/pseudo_client.h
@@ -52,9 +52,6 @@  extern FILE *pseudo_grp;
 
 /* pseudo_wrappers will try to initialize these */
 extern int (*pseudo_real_lstat)(const char *path, PSEUDO_STATBUF *buf);
-extern int (*pseudo_real_unsetenv)(const char *);
-extern char * (*pseudo_real_getenv)(const char *);
-extern int (*pseudo_real_setenv)(const char *, const char *, int);
 extern int (*pseudo_real_fork)(void);
 extern int (*pseudo_real_execv)(const char *, char * const *);
 
diff --git a/pseudo_util.c b/pseudo_util.c
index 599cf31..83f92b3 100644
--- a/pseudo_util.c
+++ b/pseudo_util.c
@@ -72,15 +72,9 @@  typedef struct {
 	char *data;
 } pseudo_evlog_entry;
 
-/* so bash overrides getenv/unsetenv/etcetera, preventing them from
- * actually modifying environ, so we have pseudo_wrappers try to dlsym
- * the right values. This could fail, in which case we'd get null
- * pointers, and we'll just call whatever the linker gives us and
- * hope for the best.
- */
-#define SETENV(x, y, z) (pseudo_real_setenv ? pseudo_real_setenv : setenv)(x, y, z)
-#define GETENV(x) (pseudo_real_getenv ? pseudo_real_getenv : getenv)(x)
-#define UNSETENV(x) (pseudo_real_unsetenv ? pseudo_real_unsetenv : unsetenv)(x)
+#define SETENV(x, y, z) setenv(x, y, z)
+#define GETENV(x) getenv(x)
+#define UNSETENV(x) unsetenv(x)
 
 #define PSEUDO_EVLOG_ENTRIES 250
 #define PSEUDO_EVLOG_LENGTH 256
diff --git a/pseudo_wrappers.c b/pseudo_wrappers.c
index 9ae1200..112239b 100644
--- a/pseudo_wrappers.c
+++ b/pseudo_wrappers.c
@@ -173,12 +173,6 @@  pseudo_init_wrappers(void) {
 	pseudo_real_fsetxattr = real_fsetxattr;
 #endif
 	pseudo_real_lstat = base_lstat;
-	/* bash has its own local copies of these which it uses
-	 * instead of ours...
-	 */
-	pseudo_real_unsetenv = dlsym(RTLD_NEXT, "unsetenv");
-	pseudo_real_getenv = dlsym(RTLD_NEXT, "getenv");
-	pseudo_real_setenv = dlsym(RTLD_NEXT, "setenv");
 	/* and these are used so the client's server spawn can bypass
 	 * wrappers.
 	 */