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a=ed25519; pk=tC3hNkJQTpNX/gLKxTNQKDmiQl6QjBNCGKJINqAdJsE= X-Developer-Signature: v=1; a=ed25519-sha256; t=1711662288; l=3778; i=justinstitt@google.com; s=20230717; h=from:subject:message-id; bh=k417LjfbcYWy0JXyEndKeFzdq4t+prtqtds4CmFz9lE=; b=bUcsODvsW82HxT9AF59CYkfSTLvtdhYAG5vjykdkAa5z+oe8P7sr0n7b1jPq1t6KP4WOaNtpP 7pqRhlsI2tvAWt+TDwXo1Bb97u3nl2QZdF+inSPrhT9m62JS+221OM8 X-Mailer: b4 0.12.3 Message-ID: <20240328-strncpy-fs-smb-client-cifssmb-c-v1-1-30d12bcf500d@google.com> Subject: [PATCH] smb: client: replace deprecated strncpy with strscpy From: Justin Stitt To: Steve French , Paulo Alcantara , Ronnie Sahlberg , Shyam Prasad N , Tom Talpey , Bharath SM Cc: linux-cifs@vger.kernel.org, samba-technical@lists.samba.org, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org, Justin Stitt 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 Reviewed-by: Kees Cook --- 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 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; }