On 22. Jun 2024, at 03:06, Rich Felker <dalias@libc.org> wrote:

On Thu, May 23, 2024 at 04:28:03PM -0400, Rich Felker wrote:

On Fri, May 10, 2024 at 06:01:58PM +0200, Florian Ziesche wrote:

Hi,

this patch increases the buffer size by one in get_lfs64() so that it
works with posix_fallocate64.
"posix_fallocate64" is 17 characters long, so 16 is one too short.

Simplified example:
before: https://compiler-explorer.com/z/4qcPhcaWr
after: https://compiler-explorer.com/z/scGvhddKW

---
diff --git a/ldso/dynlink.c b/ldso/dynlink.c
index 42687da2..8707ae1c 100644
--- a/ldso/dynlink.c
+++ b/ldso/dynlink.c
@@ -363,7 +363,7 @@ static struct symdef get_lfs64(const char *name)
        "stat\0statfs\0statvfs\0tmpfile\0truncate\0versionsort\0"
        "__fxstat\0__fxstatat\0__lxstat\0__xstat\0";
    size_t l;
-    char buf[16];
+    char buf[17];
    for (l=0; name[l]; l++) {
        if (l >= sizeof buf) goto nomatch;
        buf[l] = name[l];

Thanks for catching this. I questioned whether the 17 is sufficient,
but indeed the buffer is never nul terminated except when removing the
64, so it should be ok.

I think I'll apply your patch as a direct fix, but the whole copying
operation is unnecessary and I'll probably remove it. It works just as
well to strncmp and pass p instead of buf to find_sym, so that a
mutable copy of the name to lookup is never needed.

Applied. Does the attached look ok to get rid of the copy entirely? It
passed basic smoke testing here.

<get_lfs64.diff>