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Date: Sun, 2 Sep 2018 13:42:26 -0400
From: "Joseph C. Sible" <josephcsible@...il.com>
To: musl@...ts.openwall.com
Subject: Re: [PATCH] fexecve: implement in terms of execveat when it exists
On Sun, Sep 2, 2018 at 1:11 PM Rich Felker <dalias@...c.org> wrote:
>
> On Sun, Sep 02, 2018 at 12:04:55AM -0400, Joseph Sible wrote:
> > This lets fexecve work even when /proc isn't mounted.
> > ---
> > src/process/fexecve.c | 7 +++++++
> > 1 file changed, 7 insertions(+)
> >
> > diff --git a/src/process/fexecve.c b/src/process/fexecve.c
> > index 6507b42..905487e 100644
> > --- a/src/process/fexecve.c
> > +++ b/src/process/fexecve.c
> > @@ -1,13 +1,20 @@
> > +#define _GNU_SOURCE
> > #include <unistd.h>
> > #include <errno.h>
> > +#include <fcntl.h>
> > +#include "syscall.h"
> >
> > void __procfdname(char *, unsigned);
> >
> > int fexecve(int fd, char *const argv[], char *const envp[])
> > {
> > +#ifdef SYS_execveat
> > + return syscall(SYS_execveat, fd, "", argv, envp, AT_EMPTY_PATH);
> > +#else
> > char buf[15 + 3*sizeof(int)];
> > __procfdname(buf, fd);
> > execve(buf, argv, envp);
> > if (errno == ENOENT) errno = EBADF;
> > return -1;
> > +#endif
> > }
> > --
> > 2.7.4
>
> This breaks programs running on any kernel older than 3.19.
>
> Instead it needs to be something like
>
> int r = __syscall(SYS_execveat, fd, "", argv, envp, AT_EMPTY_PATH);
> if (r!=-ENOSYS) return __syscall_ret(r);
> ...
>
> with no #ifdef. #ifdef SYS_anything is only valid in musl when the
> existence of the syscall is arch-specific. The defines come from musl
> itself, so trying to use it for something version-specific does not
> make sense; it would be unconditionally true or false.
>
> Rich
Good catch. Updated patch below.
-- >8 --
Subject: [PATCH v2] fexecve: implement in terms of execveat when it exists
This lets fexecve work even when /proc isn't mounted.
---
src/process/fexecve.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/src/process/fexecve.c b/src/process/fexecve.c
index 6507b42..5cac05e 100644
--- a/src/process/fexecve.c
+++ b/src/process/fexecve.c
@@ -1,10 +1,15 @@
+#define _GNU_SOURCE
#include <unistd.h>
#include <errno.h>
+#include <fcntl.h>
+#include "syscall.h"
void __procfdname(char *, unsigned);
int fexecve(int fd, char *const argv[], char *const envp[])
{
+ int r = __syscall(SYS_execveat, fd, "", argv, envp, AT_EMPTY_PATH);
+ if(r != -ENOSYS) return __syscall_ret(r);
char buf[15 + 3*sizeof(int)];
__procfdname(buf, fd);
execve(buf, argv, envp);
--
2.7.4
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