[PATCH] libdwfl: fix crash when reading link map

[Omar Sandoval <osandov@osandov.com>]

From: Omar Sandoval <osandov@fb.com>

When read_addrs() was converted was converted from a nested function to
a normal function, there was a mistake in converting "buffer" from a
closure variable to a parameter: we are checking whether the pointer
argument is NULL, not whether the buffer itself is NULL. This causes a
NULL pointer dereference when we try to use the NULL buffer later.

Fixes: 3bf41d458fb6 ("link_map: Pull read_addrs() into file scope") made
Signed-off-by: Omar Sandoval <osandov@fb.com>
---
 libdwfl/ChangeLog  | 4 ++++
 libdwfl/link_map.c | 2 +-
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/libdwfl/ChangeLog b/libdwfl/ChangeLog
index fedf65a4..c57c7708 100644
--- a/libdwfl/ChangeLog
+++ b/libdwfl/ChangeLog
@@ -1,3 +1,7 @@
+2021-06-09  Omar Sandoval  <osandov@fb.com>
+
+	* link_map.c (read_addrs): Fix crash.
+
 2021-04-19  Martin Liska  <mliska@suse.cz>
 
 	* dwfl_frame.c (dwfl_attach_state): Use startswith.
diff --git a/libdwfl/link_map.c b/libdwfl/link_map.c
index 0d8d1c17..1e7d4502 100644
--- a/libdwfl/link_map.c
+++ b/libdwfl/link_map.c
@@ -254,7 +254,7 @@ read_addrs (struct memory_closure *closure,
   Dwfl *dwfl = closure->dwfl;
 
   /* Read a new buffer if the old one doesn't cover these words.  */
-  if (buffer == NULL
+  if (*buffer == NULL
       || vaddr < *read_vaddr
       || vaddr - (*read_vaddr) + nb > *buffer_available)
     {
-- 
2.32.0