RE: [PATCH v4] ceph: bound encrypted snapshot suffix formatting

[Viacheslav Dubeyko]

On Fri, 2026-04-10 at 20:40 +0000, Viacheslav Dubeyko wrote:
> On Thu, 2026-04-09 at 18:09 +0000, Viacheslav Dubeyko wrote:
> > On Thu, 2026-04-09 at 10:39 +0800, Pengpeng Hou wrote:
> > > ceph_encode_encrypted_dname() base64-encodes the encrypted snapshot
> > > name into the caller buffer and then, for long snapshot names, appends
> > > _<ino> with sprintf(p + elen, ...).
> > > 
> > > Some callers only provide NAME_MAX bytes. For long snapshot names, a
> > > large inode suffix can push the final encoded name past NAME_MAX even
> > > though the encrypted prefix stayed within the documented 240-byte
> > > budget.
> > > 
> > > Format the suffix into a small local buffer first and reject names
> > > whose suffix would exceed the caller's NAME_MAX output buffer.
> > > 
> > > Signed-off-by: Pengpeng Hou <pengpeng@xxxxxxxxxxx>
> > > ---
> > > Changes since v3:
> > > - reject `elen > 240` explicitly instead of relying only on the earlier
> > >   `WARN_ON()`
> > > - rewrite the NAME_MAX bound check in terms of the final total length
> > >   instead of `NAME_MAX - prefix_len - elen`
> > > 
> > >  fs/ceph/crypto.c | 31 +++++++++++++++++++++++++++++--
> > >  1 file changed, 29 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/fs/ceph/crypto.c b/fs/ceph/crypto.c
> > > index f3de43ccb470..42e3fff34697 100644
> > > --- a/fs/ceph/crypto.c
> > > +++ b/fs/ceph/crypto.c
> > > @@ -15,6 +15,12 @@
> > >  #include "mds_client.h"
> > >  #include "crypto.h"
> > >  
> > > +/*
> > > + * Reserve room for '_' + decimal 64-bit inode number + trailing NUL.
> > > + * ceph_encode_encrypted_dname() copies only the visible suffix bytes.
> > > + */
> > > +#define CEPH_ENCRYPTED_SNAP_INO_SUFFIX_MAX	sizeof("_18446744073709551615")
> > > +
> > >  static int ceph_crypt_get_context(struct inode *inode, void *ctx, size_t len)
> > >  {
> > >  	struct ceph_inode_info *ci = ceph_inode(inode);
> > > @@ -209,6 +215,7 @@ int ceph_encode_encrypted_dname(struct inode *parent, char *buf, int elen)
> > >  	struct inode *dir = parent;
> > >  	char *p = buf;
> > >  	u32 len;
> > > +	int prefix_len = 0;
> > >  	int name_len = elen;
> > >  	int ret;
> > >  	u8 *cryptbuf = NULL;
> > > @@ -219,6 +226,7 @@ int ceph_encode_encrypted_dname(struct inode *parent, char *buf, int elen)
> > >  		if (IS_ERR(dir))
> > >  			return PTR_ERR(dir);
> > >  		p++; /* skip initial '_' */
> > > +		prefix_len = 1;
> > >  	}
> > >  
> > >  	if (!fscrypt_has_encryption_key(dir))
> > > @@ -271,8 +279,27 @@ int ceph_encode_encrypted_dname(struct inode *parent, char *buf, int elen)
> > >  
> > >  	/* To understand the 240 limit, see CEPH_NOHASH_NAME_MAX comments */
> > >  	WARN_ON(elen > 240);
> > > -	if (dir != parent) // leading _ is already there; append _<inum>
> > > -		elen += 1 + sprintf(p + elen, "_%ld", dir->i_ino);
> > > +	if (elen > 240) {
> > > +		elen = -ENAMETOOLONG;
> > > +		goto out;
> > > +	}
> > > +
> > > +	if (dir != parent) {
> > > +		int total_len;
> > > +		/* leading '_' is already there; append _<inum> */
> > > +		char suffix[CEPH_ENCRYPTED_SNAP_INO_SUFFIX_MAX];
> > > +
> > > +		ret = snprintf(suffix, sizeof(suffix), "_%lu", dir->i_ino);
> > > +		total_len = prefix_len + elen + ret;
> > > +		if (total_len > NAME_MAX) {
> > > +			elen = -ENAMETOOLONG;
> > > +			goto out;
> > > +		}
> > > +
> > > +		memcpy(p + elen, suffix, ret);
> > > +		/* Include the leading '_' skipped by p. */
> > > +		elen = total_len;
> > > +	}
> > >  
> > >  out:
> > >  	kfree(cryptbuf);
> > 
> > Looks good.
> > 
> > Reviewed-by: Viacheslav Dubeyko <Slava.Dubeyko@xxxxxxx>
> > 
> > Let me run xfstests for the patch to double check that everything is OK. I'll
> > share the result ASAP.
> > 
> 
> The xfstests run was successful. I don't see any issues with the patch.
> 
> Tested-by: Viacheslav Dubeyko <Slava.Dubeyko@xxxxxxx>
> 
> 

Applied on testing branch of CephFS kernel client git tree.

Thanks,
Slava.