Re: [RFC PATCH 6/6 6.6] libfs: fix infinite directory reads for offset dir

Hi,

在 2024/11/11 8:52, cel@kernel.org 写道:

From: yangerkun yangerkun@huawei.com

[ Upstream commit 64a7ce76fb901bf9f9c36cf5d681328fc0fd4b5a ]

After we switch tmpfs dir operations from simple_dir_operations to simple_offset_dir_operations, every rename happened will fill new dentry to dest dir's maple tree(&SHMEM_I(inode)->dir_offsets->mt) with a free key starting with octx->newx_offset, and then set newx_offset equals to free key + 1. This will lead to infinite readdir combine with rename happened at the same time, which fail generic/736 in xfstests(detail show as below).

1. create 5000 files(1 2 3...) under one dir
2. call readdir(man 3 readdir) once, and get one entry
3. rename(entry, "TEMPFILE"), then rename("TEMPFILE", entry)
4. loop 2~3, until readdir return nothing or we loop too many times(tmpfs break test with the second condition)

We choose the same logic what commit 9b378f6ad48cf ("btrfs: fix infinite directory reads") to fix it, record the last_index when we open dir, and do not emit the entry which index >= last_index. The file->private_data

Please notice this requires last_index should never overflow, otherwise readdir will be messed up.

now used in offset dir can use directly to do this, and we also update the last_index when we llseek the dir file.

Fixes: a2e459555c5f ("shmem: stable directory offsets") Signed-off-by: yangerkun yangerkun@huawei.com Link: https://lore.kernel.org/r/20240731043835.1828697-1-yangerkun@huawei.com Reviewed-by: Chuck Lever chuck.lever@oracle.com [brauner: only update last_index after seek when offset is zero like Jan suggested] Signed-off-by: Christian Brauner brauner@kernel.org Link: https://nvd.nist.gov/vuln/detail/CVE-2024-46701 [ cel: adjusted to apply to origin/linux-6.6.y ] Signed-off-by: Chuck Lever chuck.lever@oracle.com

---

fs/libfs.c | 37 +++++++++++++++++++++++++------------ 1 file changed, 25 insertions(+), 12 deletions(-)

diff --git a/fs/libfs.c b/fs/libfs.c index a87005c89534..b59ff0dfea1f 100644 --- a/fs/libfs.c +++ b/fs/libfs.c @@ -449,6 +449,14 @@ void simple_offset_destroy(struct offset_ctx *octx) xa_destroy(&octx->xa); } +static int offset_dir_open(struct inode *inode, struct file *file) +{

• struct offset_ctx *ctx = inode->i_op->get_offset_ctx(inode);
• file->private_data = (void *)ctx->next_offset;
• return 0;

+}

Looks like xarray is still used.

I'm in the cc list ,so I assume you saw my set, then I don't know why you're ignoring my concerns.

1) next_offset is 32-bit and can overflow in a long-time running machine. 2) Once next_offset overflows, readdir will skip the files that offset is bigger.

Thanks, Kuai

• /**
  • offset_dir_llseek - Advance the read position of a directory descriptor
  • @file: an open directory whose position is to be updated

@@ -462,6 +470,9 @@ void simple_offset_destroy(struct offset_ctx *octx) */ static loff_t offset_dir_llseek(struct file *file, loff_t offset, int whence) {

• struct inode *inode = file->f_inode;
• struct offset_ctx *ctx = inode->i_op->get_offset_ctx(inode);
• switch (whence) { case SEEK_CUR: offset += file->f_pos;

@@ -475,8 +486,9 @@ static loff_t offset_dir_llseek(struct file *file, loff_t offset, int whence) } /* In this case, ->private_data is protected by f_pos_lock */

• file->private_data = NULL;
• return vfs_setpos(file, offset, U32_MAX);

• if (!offset)

• file->private_data = (void *)ctx->next_offset;
  

• return vfs_setpos(file, offset, LONG_MAX); }

static struct dentry *offset_find_next(struct xa_state *xas) @@ -505,7 +517,7 @@ static bool offset_dir_emit(struct dir_context *ctx, struct dentry *dentry) 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, long last_index) { struct offset_ctx *so_ctx = inode->i_op->get_offset_ctx(inode); XA_STATE(xas, &so_ctx->xa, ctx->pos); @@ -514,17 +526,21 @@ static void *offset_iterate_dir(struct inode *inode, struct dir_context *ctx) while (true) { dentry = offset_find_next(&xas); if (!dentry)

• 	return ERR_PTR(-ENOENT);
  

• 	return;
  

• if (dentry2offset(dentry) >= last_index) {
  

• 	dput(dentry);
  

• 	return;
  

• }
  

if (!offset_dir_emit(ctx, dentry)) { dput(dentry);

• 	break;
  

• 	return;
  

  }

dput(dentry); ctx->pos = xas.xa_index + 1; }

• return NULL; }

/** @@ -551,22 +567,19 @@ static void *offset_iterate_dir(struct inode *inode, struct dir_context *ctx) static int offset_readdir(struct file *file, struct dir_context *ctx) { struct dentry *dir = file->f_path.dentry;

• long last_index = (long)file->private_data;

lockdep_assert_held(&d_inode(dir)->i_rwsem); 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);

• offset_iterate_dir(d_inode(dir), ctx, last_index); return 0; }

const struct file_operations simple_offset_dir_operations = {

• .open = offset_dir_open, .llseek = offset_dir_llseek, .iterate_shared = offset_readdir, .read = generic_read_dir,