kexec: copy only happens before uchunk goes to zero

When loading segments, ubytes is <= mbytes.  When ubytes is exhausted,
there could be remaining mbytes.  Then in the while loop, the buf pointer
advancing with mchunk will causing meaningless reading even though it
doesn't harm.

So let's change to make sure that all of the copying and the rest only
happens before uchunk goes to zero.

Link: https://lkml.kernel.org/r/20240222092119.5602-1-gaoshanliukou@163.com
Signed-off-by: yang.zhang <yang.zhang@hexintek.com>
Acked-by: Baoquan He <bhe@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
index d08fc7b5db97905b3728b54aa37aa1492b60b1ee..2fc3d0e3715aeeac2854e7577c930b42ec5bb8c4 100644 (file)
--- a/kernel/kexec_core.c
+++ b/kernel/kexec_core.c
@@ -800,22 +800,24 @@ static int kimage_load_normal_segment(struct kimage *image,
                                PAGE_SIZE - (maddr & ~PAGE_MASK));
                uchunk = min(ubytes, mchunk);
 
-               /* For file based kexec, source pages are in kernel memory */
-               if (image->file_mode)
-                       memcpy(ptr, kbuf, uchunk);
-               else
-                       result = copy_from_user(ptr, buf, uchunk);
+               if (uchunk) {
+                       /* For file based kexec, source pages are in kernel memory */
+                       if (image->file_mode)
+                               memcpy(ptr, kbuf, uchunk);
+                       else
+                               result = copy_from_user(ptr, buf, uchunk);
+                       ubytes -= uchunk;
+                       if (image->file_mode)
+                               kbuf += uchunk;
+                       else
+                               buf += uchunk;
+               }
                kunmap_local(ptr);
                if (result) {
                        result = -EFAULT;
                        goto out;
                }
-               ubytes -= uchunk;
                maddr  += mchunk;
-               if (image->file_mode)
-                       kbuf += mchunk;
-               else
-                       buf += mchunk;
                mbytes -= mchunk;
 
                cond_resched();
@@ -866,11 +868,18 @@ static int kimage_load_crash_segment(struct kimage *image,
                        memset(ptr + uchunk, 0, mchunk - uchunk);
                }
 
-               /* For file based kexec, source pages are in kernel memory */
-               if (image->file_mode)
-                       memcpy(ptr, kbuf, uchunk);
-               else
-                       result = copy_from_user(ptr, buf, uchunk);
+               if (uchunk) {
+                       /* For file based kexec, source pages are in kernel memory */
+                       if (image->file_mode)
+                               memcpy(ptr, kbuf, uchunk);
+                       else
+                               result = copy_from_user(ptr, buf, uchunk);
+                       ubytes -= uchunk;
+                       if (image->file_mode)
+                               kbuf += uchunk;
+                       else
+                               buf += uchunk;
+               }
                kexec_flush_icache_page(page);
                kunmap_local(ptr);
                arch_kexec_pre_free_pages(page_address(page), 1);
@@ -878,12 +887,7 @@ static int kimage_load_crash_segment(struct kimage *image,
                        result = -EFAULT;
                        goto out;
                }
-               ubytes -= uchunk;
                maddr  += mchunk;
-               if (image->file_mode)
-                       kbuf += mchunk;
-               else
-                       buf += mchunk;
                mbytes -= mchunk;
 
                cond_resched();