6.12-stable review patch. If anyone has any objections, please let me know.
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From: Chuck Lever chuck.lever@oracle.com
commit 68a3a65003145644efcbb651e91db249ccd96281 upstream.
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 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 @@ -241,9 +241,15 @@ 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, long offset) @@ -287,7 +293,8 @@ int simple_offset_add(struct offset_ctx return -EBUSY;
ret = mtree_alloc_cyclic(&octx->mt, &offset, dentry, DIR_OFFSET_MIN, - LONG_MAX, &octx->next_offset, GFP_KERNEL); + DIR_OFFSET_MAX, &octx->next_offset, + GFP_KERNEL); if (unlikely(ret < 0)) return ret == -EBUSY ? -ENOSPC : ret;
@@ -443,8 +450,6 @@ 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, LONG_MAX); }
@@ -454,7 +459,7 @@ static struct dentry *offset_find_next(s struct dentry *child, *found = NULL;
rcu_read_lock(); - child = mas_find(&mas, LONG_MAX); + child = mas_find(&mas, DIR_OFFSET_MAX); if (!child) goto out; spin_lock(&child->d_lock); @@ -475,7 +480,7 @@ 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; @@ -483,7 +488,7 @@ 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); @@ -493,7 +498,10 @@ static void *offset_iterate_dir(struct i ctx->pos = dentry2offset(dentry) + 1; dput(dentry); } - return NULL; + return; + +out_eod: + ctx->pos = DIR_OFFSET_EOD; }
/** @@ -513,6 +521,8 @@ 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 @@ -525,13 +535,8 @@ 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; }