path: root/src/dirent
diff options
authorRich Felker <>2018-07-18 13:25:48 -0400
committerRich Felker <>2018-07-18 13:34:34 -0400
commitb3fa0f2b1b8c267c1cbe8c62464e484f3a174a4e (patch)
tree7d5c1d52617b69d62ddf4fbba48c2aaabeb8290a /src/dirent
parentdf6d9450ea19fd71e52cf5cdb4c85beb73066394 (diff)
fix regression in alignment of dirent structs produced by readdir
commit 32482f61da7650ff10741bd5aedd66bbc3ea165b reduced the number of int members before the dirent buf from 4 to 3, thereby misaligning it mod sizeof(off_t), producing invalid accesses on any arch where alignof(off_t)==sizeof(off_t). rather than re-adding wasted padding, reorder the struct to meet the requirement and add a comment and static assertion to prevent this from getting broken again.
Diffstat (limited to 'src/dirent')
2 files changed, 7 insertions, 1 deletions
diff --git a/src/dirent/__dirent.h b/src/dirent/__dirent.h
index 101b0368..828a5f17 100644
--- a/src/dirent/__dirent.h
+++ b/src/dirent/__dirent.h
@@ -1,9 +1,11 @@
struct __dirstream
- int fd;
off_t tell;
+ int fd;
int buf_pos;
int buf_end;
volatile int lock[1];
+ /* Any changes to this struct must preserve the property:
+ * offsetof(struct __dirent, buf) % sizeof(off_t) == 0 */
char buf[2048];
diff --git a/src/dirent/readdir.c b/src/dirent/readdir.c
index 2cf0632c..dc5f3edb 100644
--- a/src/dirent/readdir.c
+++ b/src/dirent/readdir.c
@@ -1,9 +1,13 @@
#include <dirent.h>
#include <errno.h>
+#include <stddef.h>
#include "__dirent.h"
#include "syscall.h"
#include "libc.h"
+typedef char dirstream_buf_alignment_check[1-2*(int)(
+ offsetof(struct __dirstream, buf) % sizeof(off_t))];
int __getdents(int, struct dirent *, size_t);
struct dirent *readdir(DIR *dir)