| Message ID | 20240328-strncpy-fs-smb-client-cifssmb-c-v1-1-30d12bcf500d@google.com |
|---|---|
| State | New |
| Headers | show |
| Series | smb: client: replace deprecated strncpy with strscpy | expand |
On Thu, Mar 28, 2024 at 09:44:48PM +0000, Justin Stitt wrote: > strncpy() is deprecated for use on NUL-terminated destination strings > [1] and as such we should prefer more robust and less ambiguous string > interfaces. > > In cifssmb.c: > Using strncpy with a length argument equal to strlen(src) is generally > dangerous because it can cause string buffers to not be NUL-terminated. > In this case, however, there was extra effort made to ensure the buffer > was NUL-terminated via a manual NUL-byte assignment. In an effort to rid > the kernel of strncpy() use, let's swap over to using strscpy() which > guarantees NUL-termination on the destination buffer. > > To handle the case where ea_name is NULL, let's use the ?: operator to > substitute in an empty string, thereby allowing strscpy to still > NUL-terminate the destintation string. Yeah. And for the non-NULL case, namelen is 0-255. And 255 comes from strnlen() as the limit of characters, so namelen + 1 will include the NUL terminator. > Interesting note: this flex array buffer may go on to also have some > value encoded after the NUL-termination: > | if (ea_value_len) > | memcpy(parm_data->list.name + name_len + 1, > | ea_value, ea_value_len); > > Now for smb2ops.c and smb2transport.c: > Both of these cases are simple, strncpy() is used to copy string > literals which have a length less than the destination buffer's size. We > can simply swap in the new 2-argument version of strscpy() introduced in > Commit e6584c3964f2f ("string: Allow 2-argument strscpy()"). > > Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1] > Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2] > Link: https://github.com/KSPP/linux/issues/90 > Cc: linux-hardening@vger.kernel.org > Signed-off-by: Justin Stitt <justinstitt@google.com> Reviewed-by: Kees Cook <keescook@chromium.org>
diff --git a/fs/smb/client/cifssmb.c b/fs/smb/client/cifssmb.c index 5aee55551573..23b5709ddc31 100644 --- a/fs/smb/client/cifssmb.c +++ b/fs/smb/client/cifssmb.c @@ -5854,10 +5854,8 @@ CIFSSMBSetEA(const unsigned int xid, struct cifs_tcon *tcon, parm_data->list.EA_flags = 0; /* we checked above that name len is less than 255 */ parm_data->list.name_len = (__u8)name_len; - /* EA names are always ASCII */ - if (ea_name) - strncpy(parm_data->list.name, ea_name, name_len); - parm_data->list.name[name_len] = '\0'; + /* EA names are always ASCII and NUL-terminated */ + strscpy(parm_data->list.name, ea_name ?: "", name_len + 1); parm_data->list.value_len = cpu_to_le16(ea_value_len); /* caller ensures that ea_value_len is less than 64K but we need to ensure that it fits within the smb */ diff --git a/fs/smb/client/smb2ops.c b/fs/smb/client/smb2ops.c index 2ed456948f34..35bf7eb315cd 100644 --- a/fs/smb/client/smb2ops.c +++ b/fs/smb/client/smb2ops.c @@ -3913,7 +3913,7 @@ smb21_set_oplock_level(struct cifsInodeInfo *cinode, __u32 oplock, strcat(message, "W"); } if (!new_oplock) - strncpy(message, "None", sizeof(message)); + strscpy(message, "None"); cinode->oplock = new_oplock; cifs_dbg(FYI, "%s Lease granted on inode %p\n", message, diff --git a/fs/smb/client/smb2transport.c b/fs/smb/client/smb2transport.c index 5a3ca62d2f07..1d6e54f7879e 100644 --- a/fs/smb/client/smb2transport.c +++ b/fs/smb/client/smb2transport.c @@ -659,7 +659,7 @@ smb2_sign_rqst(struct smb_rqst *rqst, struct TCP_Server_Info *server) } spin_unlock(&server->srv_lock); if (!is_binding && !server->session_estab) { - strncpy(shdr->Signature, "BSRSPYL", 8); + strscpy(shdr->Signature, "BSRSPYL"); return 0; }
strncpy() is deprecated for use on NUL-terminated destination strings [1] and as such we should prefer more robust and less ambiguous string interfaces. In cifssmb.c: Using strncpy with a length argument equal to strlen(src) is generally dangerous because it can cause string buffers to not be NUL-terminated. In this case, however, there was extra effort made to ensure the buffer was NUL-terminated via a manual NUL-byte assignment. In an effort to rid the kernel of strncpy() use, let's swap over to using strscpy() which guarantees NUL-termination on the destination buffer. To handle the case where ea_name is NULL, let's use the ?: operator to substitute in an empty string, thereby allowing strscpy to still NUL-terminate the destintation string. Interesting note: this flex array buffer may go on to also have some value encoded after the NUL-termination: | if (ea_value_len) | memcpy(parm_data->list.name + name_len + 1, | ea_value, ea_value_len); Now for smb2ops.c and smb2transport.c: Both of these cases are simple, strncpy() is used to copy string literals which have a length less than the destination buffer's size. We can simply swap in the new 2-argument version of strscpy() introduced in Commit e6584c3964f2f ("string: Allow 2-argument strscpy()"). Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1] Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2] Link: https://github.com/KSPP/linux/issues/90 Cc: linux-hardening@vger.kernel.org Signed-off-by: Justin Stitt <justinstitt@google.com> --- fs/smb/client/cifssmb.c | 6 ++---- fs/smb/client/smb2ops.c | 2 +- fs/smb/client/smb2transport.c | 2 +- 3 files changed, 4 insertions(+), 6 deletions(-) --- base-commit: 928a87efa42302a23bb9554be081a28058495f22 change-id: 20240328-strncpy-fs-smb-client-cifssmb-c-952d43af06d8 Best regards, -- Justin Stitt <justinstitt@google.com>