`struct dirent' returned from readdir(3) could be shorter (or longer)
than `sizeof(struct dirent)', thus memcpy of sizeof length will overread
into unallocated page causing SIGSEGV. Example stack trace:
#0 0x00005555559ebeed v9fs_co_readdir_many (/usr/bin/qemu-system-x86_64 + 0x497eed)
#1 0x00005555559ec2e9 v9fs_readdir (/usr/bin/qemu-system-x86_64 + 0x4982e9)
#2 0x0000555555eb7983 coroutine_trampoline (/usr/bin/qemu-system-x86_64 + 0x963983)
#3 0x00007ffff73e0be0 n/a (n/a + 0x0)
While fixing this, provide a helper for any future `struct dirent' cloning.
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/841
Cc: qemu-stable@nongnu.org
Co-authored-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
Reviewed-by: Dmitry V. Levin <ldv@altlinux.org>
Signed-off-by: Vitaly Chikunov <vt@altlinux.org>
Tested-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
Reviewed-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
Acked-by: Greg Kurz <groug@kaod.org>
Tested-by: Vitaly Chikunov <vt@altlinux.org>
Message-Id: <
20220216181821.
3481527-1-vt@altlinux.org>
[C.S. - Fix typo in source comment. ]
Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
V9fsSynthOpenState *synth_open;
V9fsSynthNode *node = *(V9fsSynthNode **)fs_path->data;
- synth_open = g_malloc(sizeof(*synth_open));
+ /*
+ * V9fsSynthOpenState contains 'struct dirent' which have OS-specific
+ * properties, thus it's zero cleared on allocation here and below
+ * in synth_open.
+ */
+ synth_open = g_new0(V9fsSynthOpenState, 1);
synth_open->node = node;
node->open_count++;
fs->private = synth_open;
static void synth_direntry(V9fsSynthNode *node,
struct dirent *entry, off_t off)
{
- strcpy(entry->d_name, node->name);
+ size_t sz = strlen(node->name) + 1;
+ /*
+ * 'entry' is always inside of V9fsSynthOpenState which have NAME_MAX
+ * back padding. Ensure we do not overflow it.
+ */
+ g_assert(sizeof(struct dirent) + NAME_MAX >=
+ offsetof(struct dirent, d_name) + sz);
+ memcpy(entry->d_name, node->name, sz);
entry->d_ino = node->attr->inode;
entry->d_off = off + 1;
}
V9fsSynthOpenState *synth_open;
V9fsSynthNode *node = *(V9fsSynthNode **)fs_path->data;
- synth_open = g_malloc(sizeof(*synth_open));
+ synth_open = g_new0(V9fsSynthOpenState, 1);
synth_open->node = node;
node->open_count++;
fs->private = synth_open;
off_t offset;
V9fsSynthNode *node;
struct dirent dent;
+ /*
+ * Ensure there is enough space for 'dent' above, some systems have a
+ * d_name size of just 1, which would cause a buffer overrun.
+ */
+ char dent_trailing_space[NAME_MAX];
} V9fsSynthOpenState;
int qemu_v9fs_synth_mkdir(V9fsSynthNode *parent, int mode,
} else {
e = e->next = g_malloc0(sizeof(V9fsDirEnt));
}
- e->dent = g_malloc0(sizeof(struct dirent));
- memcpy(e->dent, dent, sizeof(struct dirent));
+ e->dent = qemu_dirent_dup(dent);
/* perform a full stat() for directory entry if requested by caller */
if (dostat) {
}
#endif /* !HAVE_SYSTEM_FUNCTION */
+/**
+ * Duplicate directory entry @dent.
+ *
+ * It is highly recommended to use this function instead of open coding
+ * duplication of @c dirent objects, because the actual @c struct @c dirent
+ * size may be bigger or shorter than @c sizeof(struct dirent) and correct
+ * handling is platform specific (see gitlab issue #841).
+ *
+ * @dent - original directory entry to be duplicated
+ * @returns duplicated directory entry which should be freed with g_free()
+ */
+struct dirent *qemu_dirent_dup(struct dirent *dent);
+
#ifdef __cplusplus
}
#endif
extern int madvise(char *, size_t, int);
#endif
+#include <dirent.h>
#include "qemu-common.h"
#include "qemu/cutils.h"
#include "qemu/sockets.h"
return readv_writev(fd, iov, iov_cnt, true);
}
#endif
+
+struct dirent *
+qemu_dirent_dup(struct dirent *dent)
+{
+ size_t sz = 0;
+#if defined _DIRENT_HAVE_D_RECLEN
+ /* Avoid use of strlen() if platform supports d_reclen. */
+ sz = dent->d_reclen;
+#endif
+ /*
+ * Test sz for zero even if d_reclen is available
+ * because some drivers may set d_reclen to zero.
+ */
+ if (sz == 0) {
+ /* Fallback to the most portable way. */
+ sz = offsetof(struct dirent, d_name) +
+ strlen(dent->d_name) + 1;
+ }
+ return g_memdup(dent, sz);
+}