[PATCH v2 1/6] fs/readdir: Fix filldir() and filldir64() use of user_access_begin()

[Christophe Leroy]

Some architectures grand full access to userspace regardless of the
address/len passed to user_access_begin(), but other architectures
only grand access to the requested area.

For exemple, on 32 bits powerpc (book3s/32), access is granted by
segments of 256 Mbytes.

Modify filldir() and filldir64() to request the real area they need
to get access to, i.e. the area covering the parent dirent (if any)
and the contiguous current dirent.

Fixes: 9f79b78ef744 ("Convert filldir[64]() from __put_user() to unsafe_put_user()")
Signed-off-by: Christophe Leroy <christophe.leroy at c-s.fr>
---
v2: have user_access_begin() cover both parent dirent (if any) and current dirent
---
 fs/readdir.c | 50 ++++++++++++++++++++++++++++----------------------
 1 file changed, 28 insertions(+), 22 deletions(-)

diff --git a/fs/readdir.c b/fs/readdir.c
index d26d5ea4de7b..3f9b4488d9b7 100644
--- a/fs/readdir.c
+++ b/fs/readdir.c
@@ -214,7 +214,7 @@ struct getdents_callback {
 static int filldir(struct dir_context *ctx, const char *name, int namlen,
 		   loff_t offset, u64 ino, unsigned int d_type)
 {
-	struct linux_dirent __user * dirent;
+	struct linux_dirent __user * dirent, *dirent0;
 	struct getdents_callback *buf =
 		container_of(ctx, struct getdents_callback, ctx);
 	unsigned long d_ino;
@@ -232,19 +232,22 @@ static int filldir(struct dir_context *ctx, const char *name, int namlen,
 		buf->error = -EOVERFLOW;
 		return -EOVERFLOW;
 	}
-	dirent = buf->previous;
-	if (dirent && signal_pending(current))
+	dirent0 = buf->previous;
+	if (dirent0 && signal_pending(current))
 		return -EINTR;
 
-	/*
-	 * Note! This range-checks 'previous' (which may be NULL).
-	 * The real range was checked in getdents
-	 */
-	if (!user_access_begin(dirent, sizeof(*dirent)))
-		goto efault;
-	if (dirent)
-		unsafe_put_user(offset, &dirent->d_off, efault_end);
 	dirent = buf->current_dir;
+	if (dirent0) {
+		int sz = (void __user *)dirent + reclen -
+			 (void __user *)dirent0;
+
+		if (!user_access_begin(dirent0, sz))
+			goto efault;
+		unsafe_put_user(offset, &dirent0->d_off, efault_end);
+	} else {
+		if (!user_access_begin(dirent, reclen))
+			goto efault;
+	}
 	unsafe_put_user(d_ino, &dirent->d_ino, efault_end);
 	unsafe_put_user(reclen, &dirent->d_reclen, efault_end);
 	unsafe_put_user(d_type, (char __user *) dirent + reclen - 1, efault_end);
@@ -307,7 +310,7 @@ struct getdents_callback64 {
 static int filldir64(struct dir_context *ctx, const char *name, int namlen,
 		     loff_t offset, u64 ino, unsigned int d_type)
 {
-	struct linux_dirent64 __user *dirent;
+	struct linux_dirent64 __user *dirent, *dirent0;
 	struct getdents_callback64 *buf =
 		container_of(ctx, struct getdents_callback64, ctx);
 	int reclen = ALIGN(offsetof(struct linux_dirent64, d_name) + namlen + 1,
@@ -319,19 +322,22 @@ static int filldir64(struct dir_context *ctx, const char *name, int namlen,
 	buf->error = -EINVAL;	/* only used if we fail.. */
 	if (reclen > buf->count)
 		return -EINVAL;
-	dirent = buf->previous;
-	if (dirent && signal_pending(current))
+	dirent0 = buf->previous;
+	if (dirent0 && signal_pending(current))
 		return -EINTR;
 
-	/*
-	 * Note! This range-checks 'previous' (which may be NULL).
-	 * The real range was checked in getdents
-	 */
-	if (!user_access_begin(dirent, sizeof(*dirent)))
-		goto efault;
-	if (dirent)
-		unsafe_put_user(offset, &dirent->d_off, efault_end);
 	dirent = buf->current_dir;
+	if (dirent0) {
+		int sz = (void __user *)dirent + reclen -
+			 (void __user *)dirent0;
+
+		if (!user_access_begin(dirent0, sz))
+			goto efault;
+		unsafe_put_user(offset, &dirent0->d_off, efault_end);
+	} else {
+		if (!user_access_begin(dirent, reclen))
+			goto efault;
+	}
 	unsafe_put_user(ino, &dirent->d_ino, efault_end);
 	unsafe_put_user(reclen, &dirent->d_reclen, efault_end);
 	unsafe_put_user(d_type, &dirent->d_type, efault_end);
-- 
2.25.0