Patch "libfs: Replace simple_offset end-of-directory detection" has been added to the 6.6-stable tree

gregkh
2025-01-30T09:00:05Z

This is a note to let you know that I've just added the patch titled

libfs: Replace simple_offset end-of-directory detection

to the 6.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
libfs-replace-simple_offset-end-of-directory-detection.patch
and it can be found in the queue-6.6 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.

From stable+bounces-110409-greg=kroah.com@vger.kernel.org Fri Jan 24 20:22:03 2025
From: cel@kernel.org
Date: Fri, 24 Jan 2025 14:19:44 -0500
Subject: libfs: Replace simple_offset end-of-directory detection
To: Hugh Dickins <hughd@google.com>, Andrew Morten <akpm@linux-foundation.org>, Christian Brauner <brauner@kernel.org>, Al Viro <viro@zeniv.linux.org.uk>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Sasha Levin <sashal@kernel.org>
Cc: <linux-fsdevel@vger.kernel.org>, <stable@vger.kernel.org>, <linux-mm@kvack.org>, yukuai3@huawei.com, yangerkun@huawei.com, Chuck Lever <chuck.lever@oracle.com>
Message-ID: <20250124191946.22308-10-cel@kernel.org>

From: Chuck Lever <chuck.lever@oracle.com>

[ Upstream commit 68a3a65003145644efcbb651e91db249ccd96281 ]

According to getdents(3), the d_off field in each returned directory
entry points to the next entry in the directory. The d_off field in
the last returned entry in the readdir buffer must contain a valid
offset value, but if it points to an actual directory entry, then
readdir/getdents can loop.

This patch introduces a specific fixed offset value that is placed
in the d_off field of the last entry in a directory. Some user space
applications assume that the EOD offset value is larger than the
offsets of real directory entries, so the largest valid offset value
is reserved for this purpose. This new value is never allocated by
simple_offset_add().

When ->iterate_dir() returns, getdents{64} inserts the ctx->pos
value into the d_off field of the last valid entry in the readdir
buffer. When it hits EOD, offset_readdir() sets ctx->pos to the EOD
offset value so the last entry is updated to point to the EOD marker.

When trying to read the entry at the EOD offset, offset_readdir()
terminates immediately.

It is worth noting that using a Maple tree for directory offset
value allocation does not guarantee a 63-bit range of values --
on platforms where "long" is a 32-bit type, the directory offset
value range is still 0..(2^31 - 1). For broad compatibility with
32-bit user space, the largest tmpfs directory cookie value is now
S32_MAX.

Fixes: 796432efab1e ("libfs: getdents() should return 0 after reaching EOD")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Link: https://lore.kernel.org/r/20241228175522.1854234-5-cel@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
[ cel: adjusted to apply to origin/linux-6.6.y ]
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/libfs.c | 37 +++++++++++++++++++++----------------
1 file changed, 21 insertions(+), 16 deletions(-)

--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -239,9 +239,15 @@ const struct inode_operations simple_dir
};
EXPORT_SYMBOL(simple_dir_inode_operations);

-/* 0 is '.', 1 is '..', so always start with offset 2 or more */
+/* simple_offset_add() never assigns these to a dentry */
enum {
- DIR_OFFSET_MIN = 2,
+ DIR_OFFSET_EOD = S32_MAX,
+};
+
+/* simple_offset_add() allocation range */
+enum {
+ DIR_OFFSET_MIN = 2,
+ DIR_OFFSET_MAX = DIR_OFFSET_EOD - 1,
};

static void offset_set(struct dentry *dentry, u32 offset)
@@ -278,7 +284,8 @@ void simple_offset_init(struct offset_ct
*/
int simple_offset_add(struct offset_ctx *octx, struct dentry *dentry)
{
- static const struct xa_limit limit = XA_LIMIT(DIR_OFFSET_MIN, U32_MAX);
+ static const struct xa_limit limit = XA_LIMIT(DIR_OFFSET_MIN,
+ DIR_OFFSET_MAX);
u32 offset;
int ret;

@@ -442,8 +449,6 @@ static loff_t offset_dir_llseek(struct f
return -EINVAL;
}

- /* In this case, ->private_data is protected by f_pos_lock */
- file->private_data = NULL;
return vfs_setpos(file, offset, U32_MAX);
}

@@ -453,7 +458,7 @@ static struct dentry *offset_find_next(s
XA_STATE(xas, &octx->xa, offset);

rcu_read_lock();
- child = xas_next_entry(&xas, U32_MAX);
+ child = xas_next_entry(&xas, DIR_OFFSET_MAX);
if (!child)
goto out;
spin_lock(&child->d_lock);
@@ -474,7 +479,7 @@ static bool offset_dir_emit(struct dir_c
inode->i_ino, fs_umode_to_dtype(inode->i_mode));
}

-static void *offset_iterate_dir(struct inode *inode, struct dir_context *ctx)
+static void offset_iterate_dir(struct inode *inode, struct dir_context *ctx)
{
struct offset_ctx *octx = inode->i_op->get_offset_ctx(inode);
struct dentry *dentry;
@@ -482,7 +487,7 @@ static void *offset_iterate_dir(struct i
while (true) {
dentry = offset_find_next(octx, ctx->pos);
if (!dentry)
- return ERR_PTR(-ENOENT);
+ goto out_eod;

if (!offset_dir_emit(ctx, dentry)) {
dput(dentry);
@@ -492,7 +497,10 @@ static void *offset_iterate_dir(struct i
ctx->pos = dentry2offset(dentry) + 1;
dput(dentry);
}
- return NULL;
+ return;
+
+out_eod:
+ ctx->pos = DIR_OFFSET_EOD;
}

/**
@@ -512,6 +520,8 @@ static void *offset_iterate_dir(struct i
*
* On return, @ctx->pos contains an offset that will read the next entry
* in this directory when offset_readdir() is called again with @ctx.
+ * Caller places this value in the d_off field of the last entry in the
+ * user's buffer.
*
* Return values:
* %0 - Complete
@@ -524,13 +534,8 @@ static int offset_readdir(struct file *f

if (!dir_emit_dots(file, ctx))
return 0;
-
- /* In this case, ->private_data is protected by f_pos_lock */
- if (ctx->pos == DIR_OFFSET_MIN)
- file->private_data = NULL;
- else if (file->private_data == ERR_PTR(-ENOENT))
- return 0;
- file->private_data = offset_iterate_dir(d_inode(dir), ctx);
+ if (ctx->pos != DIR_OFFSET_EOD)
+ offset_iterate_dir(d_inode(dir), ctx);
return 0;
}

Patches currently in stable-queue which might be from cel@kernel.org are

queue-6.6/libfs-replace-simple_offset-end-of-directory-detection.patch
queue-6.6/libfs-re-arrange-locking-in-offset_iterate_dir.patch
queue-6.6/libfs-add-simple_offset_empty.patch
queue-6.6/shmem-fix-shmem_rename2.patch
queue-6.6/revert-libfs-add-simple_offset_empty.patch
queue-6.6/libfs-use-d_children-list-to-iterate-simple_offset-directories.patch
queue-6.6/libfs-define-a-minimum-directory-offset.patch
queue-6.6/libfs-return-enospc-when-the-directory-offset-range-is-exhausted.patch
queue-6.6/libfs-fix-simple_offset_rename_exchange.patch
queue-6.6/libfs-add-simple_offset_rename-api.patch