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[PATCH] uml: make execvp safe for our usage

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Reimplement execvp for our purposes - after we call fork() it is fundamentally
unsafe to use the kernel allocator - current is not valid there.  So we simply
pass to our modified execvp() a preallocated buffer.  This fixes a real bug
and works very well in testing (I've seen indirectly warning messages from the
forked thread - they went on the pipe connected to its stdout and where read
as a number by UML, when calling read_output().  I verified the obtained
number corresponded to "BUG:").

The added use of __cant_sleep() is not a new bug since __cant_sleep() is
already used in the same function - passing an atomicity parameter would be
better but it would require huge change, stating that this function must not
be called in atomic context and can sleep is a better idea (will make sure of
this gradually).

Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Acked-by: Jeff Dike <jdike@addtoit.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Paolo 'Blaisorblade' Giarrusso
2006-11-25 11:09:39 -08:00
committed by Linus Torvalds
parent 9dce447a54
commit 5d48545e5e
4 changed files with 166 additions and 9 deletions
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14
arch/um/os-Linux/helper.c
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@@ -8,18 +8,21 @@
#include <unistd.h>
#include <errno.h>
#include <sched.h>
#include <limits.h>
#include <sys/signal.h>
#include <sys/wait.h>
#include "user.h"
#include "kern_util.h"
#include "user_util.h"
#include "os.h"
#include "um_malloc.h"
struct helper_data {
void (*pre_exec)(void*);
void *pre_data;
char **argv;
int fd;
char *buf;
};
/* Debugging aid, changed only from gdb */
@@ -41,9 +44,8 @@ static int helper_child(void *arg)
}
if (data->pre_exec != NULL)
(*data->pre_exec)(data->pre_data);
execvp(argv[0], argv);
errval = -errno;
printk("helper_child - execve of '%s' failed - errno = %d\n", argv[0], errno);
errval = execvp_noalloc(data->buf, argv[0], argv);
printk("helper_child - execvp of '%s' failed - errno = %d\n", argv[0], -errval);
os_write_file(data->fd, &errval, sizeof(errval));
kill(os_getpid(), SIGKILL);
return 0;
@@ -84,11 +86,13 @@ int run_helper(void (*pre_exec)(void *), void *pre_data, char **argv,
data.pre_data = pre_data;
data.argv = argv;
data.fd = fds[1];
data.buf = __cant_sleep() ? um_kmalloc_atomic(PATH_MAX) :
um_kmalloc(PATH_MAX);
pid = clone(helper_child, (void *) sp, CLONE_VM | SIGCHLD, &data);
if (pid < 0) {
ret = -errno;
printk("run_helper : clone failed, errno = %d\n", errno);
goto out_close;
goto out_free2;
}
close(fds[1]);
@@ -109,6 +113,8 @@ int run_helper(void (*pre_exec)(void *), void *pre_data, char **argv,
CATCH_EINTR(waitpid(pid, NULL, 0));
}
out_free2:
kfree(data.buf);
out_close:
if (fds[1] != -1)
close(fds[1]);