[glibc/release/2.35/master] linux: __get_nprocs_sched: do not feed CPU_COUNT_S with garbage [BZ #28850]

[Dmitry Levin <ldv@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=a2f1675634b3513c09c38e55e6766e8c05768b1f

commit a2f1675634b3513c09c38e55e6766e8c05768b1f
Author: Gleb Fotengauer-Malinovskiy <glebfm@altlinux.org>
Date:   Tue Feb 1 22:39:02 2022 +0000

    linux: __get_nprocs_sched: do not feed CPU_COUNT_S with garbage [BZ #28850]
    
    Pass the actual number of bytes returned by the kernel.
    
    Fixes: 33099d72e41c ("linux: Simplify get_nprocs")
    Reviewed-by: Dmitry V. Levin <ldv@altlinux.org>
    
    (cherry picked from commit 97ba273b505763325efd802dc3a9562dbba79579)

Diff:
---
 NEWS                                  | 1 +
 sysdeps/unix/sysv/linux/getsysstats.c | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/NEWS b/NEWS
index b1aae94cfb..d1602051d1 100644
--- a/NEWS
+++ b/NEWS
@@ -9,6 +9,7 @@ Version 2.35.1
 
 The following bugs are resolved with this release:
 
+  [28850] linux: __get_nprocs_sched reads uninitialized memory from the stack
   [28853] libc: tst-spawn6 changes current foreground process group
     (breaks test isolation)
 
diff --git a/sysdeps/unix/sysv/linux/getsysstats.c b/sysdeps/unix/sysv/linux/getsysstats.c
index 4798cc337e..c98c8ce3d4 100644
--- a/sysdeps/unix/sysv/linux/getsysstats.c
+++ b/sysdeps/unix/sysv/linux/getsysstats.c
@@ -44,7 +44,7 @@ __get_nprocs_sched (void)
   int r = INTERNAL_SYSCALL_CALL (sched_getaffinity, 0, cpu_bits_size,
 				 cpu_bits);
   if (r > 0)
-    return CPU_COUNT_S (cpu_bits_size, (cpu_set_t*) cpu_bits);
+    return CPU_COUNT_S (r, (cpu_set_t*) cpu_bits);
   else if (r == -EINVAL)
     /* The input buffer is still not enough to store the number of cpus.  This
        is an arbitrary values assuming such systems should be rare and there