|
Message-ID: <CAGXu5j+OTu84ohuR3f4_xKRw9vikVi-K2TnH3+n_ekX1m1Vv8A@mail.gmail.com> Date: Wed, 7 Mar 2018 09:20:31 -0800 From: Kees Cook <keescook@...omium.org> To: Rasmus Villemoes <rasmus.villemoes@...vas.dk> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, LKML <linux-kernel@...r.kernel.org>, "Tobin C. Harding" <me@...in.cc>, Tycho Andersen <tycho@...ho.ws>, Oleg Drokin <oleg.drokin@...el.com>, Andreas Dilger <andreas.dilger@...el.com>, James Simmons <jsimmons@...radead.org>, Dmitry Eremin <dmitry.eremin@...el.com>, Gargi Sharma <gs051095@...il.com>, Lustre Development List <lustre-devel@...ts.lustre.org>, devel@...verdev.osuosl.org, Kernel Hardening <kernel-hardening@...ts.openwall.com> Subject: Re: [PATCH] staging: lustre: Remove VLA usage On Wed, Mar 7, 2018 at 5:10 AM, Rasmus Villemoes <rasmus.villemoes@...vas.dk> wrote: > On 2018-03-07 06:46, Kees Cook wrote: >> The kernel would like to remove all VLA usage. This switches to a >> simple kasprintf() instead. >> >> Signed-off-by: Kees Cook <keescook@...omium.org> >> --- >> drivers/staging/lustre/lustre/llite/xattr.c | 19 +++++++++++++------ >> 1 file changed, 13 insertions(+), 6 deletions(-) >> >> diff --git a/drivers/staging/lustre/lustre/llite/xattr.c b/drivers/staging/lustre/lustre/llite/xattr.c >> index 532384c91447..aab4eab64289 100644 >> --- a/drivers/staging/lustre/lustre/llite/xattr.c >> +++ b/drivers/staging/lustre/lustre/llite/xattr.c >> @@ -87,7 +87,7 @@ ll_xattr_set_common(const struct xattr_handler *handler, >> const char *name, const void *value, size_t size, >> int flags) >> { >> - char fullname[strlen(handler->prefix) + strlen(name) + 1]; >> + char *fullname; >> struct ll_sb_info *sbi = ll_i2sbi(inode); >> struct ptlrpc_request *req = NULL; >> const char *pv = value; >> @@ -141,10 +141,13 @@ ll_xattr_set_common(const struct xattr_handler *handler, >> return -EPERM; >> } >> >> - sprintf(fullname, "%s%s\n", handler->prefix, name); > > It's probably worth pointing out that this actually fixes an > unconditional buffer overflow: fullname only has room for the two > strings and the '\n', but vsnprintf() is told that the buffer has > infinite size (well, INT_MAX), so there should be plenty of room to > append the '\0' after the '\n'. > >> + fullname = kasprintf(GFP_KERNEL, "%s%s\n", handler->prefix, name); >> + if (!fullname) >> + return -ENOMEM; >> rc = md_setxattr(sbi->ll_md_exp, ll_inode2fid(inode), >> valid, fullname, pv, size, 0, flags, >> ll_i2suppgid(inode), &req); >> + kfree(fullname); >> if (rc) { >> if (rc == -EOPNOTSUPP && handler->flags == XATTR_USER_T) { >> LCONSOLE_INFO("Disabling user_xattr feature because it is not supported on the server\n"); >> @@ -364,7 +367,7 @@ static int ll_xattr_get_common(const struct xattr_handler *handler, >> struct dentry *dentry, struct inode *inode, >> const char *name, void *buffer, size_t size) >> { >> - char fullname[strlen(handler->prefix) + strlen(name) + 1]; >> + char *fullname; >> struct ll_sb_info *sbi = ll_i2sbi(inode); >> #ifdef CONFIG_FS_POSIX_ACL >> struct ll_inode_info *lli = ll_i2info(inode); >> @@ -411,9 +414,13 @@ static int ll_xattr_get_common(const struct xattr_handler *handler, >> if (handler->flags == XATTR_ACL_DEFAULT_T && !S_ISDIR(inode->i_mode)) >> return -ENODATA; >> #endif >> - sprintf(fullname, "%s%s\n", handler->prefix, name); > > Same here. > > I'm a little surprised this hasn't been caugt by static analysis, I > thought gcc/coverity/smatch/whatnot had gotten pretty good at computing > the size of the output generated by a given format string with "known" > arguments and comparing to the size of the output buffer. Though of > course it does require the tool to be able to do symbolic manipulations, > in this case realizing that > > outsize == strlen(x)+strlen(y)+1+1 > bufsize == strlen(x)+strlen(y)+1 > > Rasmus Oh yes, hah. I didn't even see the \n in the string. :P So, both a VLA fix and a buffer over-run fix. Can I add your "Reviewed-by"? :) -Kees -- Kees Cook Pixel Security
Powered by blists - more mailing lists
Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.