[PATCH] proc/kcore: fix invalid memory access in multi-page read optimization

[Dominique Martinet]

The 'm' kcore_list item can point to kclist_head, and it is incorrect to
look at m->addr / m->size in this case.
There is no choice but to run through the list of entries for every address
if we did not find any entry in the previous iteration

Fixes: bf991c2231117 ("proc/kcore: optimize multiple page reads")
Signed-off-by: Dominique Martinet <asmadeus@xxxxxxxxxxxxx>
---

I guess now I'm looking at bf991c2231117 again that it would be slightly
more efficient to remove the !m check and initialize m to point to
kclist_head like this:
 m = list_entry(&kclist_head, struct kcore_list, list);
but it feels a bit forced to me; deferring the choice to others.

 fs/proc/kcore.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
index ad72261ee3fe..50036f6e1f52 100644
--- a/fs/proc/kcore.c
+++ b/fs/proc/kcore.c
@@ -451,7 +451,8 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
 		 * If this is the first iteration or the address is not within
 		 * the previous entry, search for a matching entry.
 		 */
-		if (!m || start < m->addr || start >= m->addr + m->size) {
+		if (!m || &m->list == &kclist_head || start < m->addr ||
+		    start >= m->addr + m->size) {
 			list_for_each_entry(m, &kclist_head, list) {
 				if (start >= m->addr &&
 				    start < m->addr + m->size)
-- 
2.17.1