On Wed, 1 Jul 2026 07:58:43 +0900 Masami Hiramatsu (Google) <[email protected]> wrote:
> On Tue, 30 Jun 2026 17:47:46 +0000 > Bradley Morgan <[email protected]> wrote: > > > When xbc_snprint_cmdline() is called during the size-probing phase > > (with buf = NULL and size = 0), the function computes the end pointer > > as 'buf + size' (NULL + 0) and repeatedly advances 'buf' via 'buf += ret'. > > > > Under the C standard, performing pointer arithmetic on a NULL pointer is > > undefined behavior. While harmless inside the kernel, this code is also > > compiled into the userspace host tool 'tools/bootconfig', where host > > compilers with UBSan or FORTIFY_SOURCE enabled abort the build when they > > detect NULL pointer arithmetic. > > > > Fix this by guarding the pointer arithmetic so 'buf' is only advanced when > > non-NULL, and track the running written length in a separate 'len' counter > > for the return value (which cannot be recovered from pointer math when > > 'buf' is NULL). The rest() helper and snprintf call sites are unchanged. > > > > Fixes: 51887d03aca1 ("bootconfig: init: Allow admin to use bootconfig for > > kernel command line") > > Cc: [email protected] > > Assisted-by: GLM:glm-5.2 > > Signed-off-by: Bradley Morgan <[email protected]> > > Thanks for the fix! > Let me pick this to bootconfig/fixes. Sorry, I eventually decided to pick Breno's fix [1], because it fixes the same issue earlier (in bootconfig/core) and has a well documented comment on the code. [1] https://lore.kernel.org/all/[email protected]/ BTW, I decided to have several branches for bootconfig and probes. bootconfig/core is a core development branch, which is the main branch. The patches in this branch is for development, including new features and fixes. (but fixes will be moved to */fixes soon.) bootconfig/fixes is for a branch to manage fixes. This will be sent to Linus soon (for urgent fix), or after releasing -rc. bootconfig/for-next is for new features or cleanups, for preparing the next merge window, and for merge test in linux-next. If you make any patches, please check the bootconfig/core at first, and check bootconfig/fixes for fix. Note: The core is usually forcibly updated, actively rebased on top of bootconfig/fixes. The for-next is not so frequently updated, but can be forced update for fixing merge conflict etc. The fixes should be solid, but if I made mistakes I will forcibly update it before sending PR. Thank you, > > Thank you, > > > --- > > lib/bootconfig.c | 13 +++++++++---- > > 1 file changed, 9 insertions(+), 4 deletions(-) > > > > Changes since v1: > > - Got the big guns out! :) (see Assisted-by). > > - Addressed review from Masami Hiramatsu and Breno Leitao. > > > > diff --git a/lib/bootconfig.c b/lib/bootconfig.c > > index f445b7703fdd..c913259c80ce 100644 > > --- a/lib/bootconfig.c > > +++ b/lib/bootconfig.c > > @@ -427,8 +427,9 @@ static char xbc_namebuf[XBC_KEYLEN_MAX] __initdata; > > int __init xbc_snprint_cmdline(char *buf, size_t size, struct xbc_node > > *root) > > { > > struct xbc_node *knode, *vnode; > > - char *end = buf + size; > > + char *end = buf ? buf + size : NULL; > > const char *val, *q; > > + size_t len = 0; > > int ret; > > > > xbc_node_for_each_key_value(root, knode, val) { > > @@ -442,7 +443,9 @@ int __init xbc_snprint_cmdline(char *buf, size_t size, > > struct xbc_node *root) > > ret = snprintf(buf, rest(buf, end), "%s ", xbc_namebuf); > > if (ret < 0) > > return ret; > > - buf += ret; > > + len += ret; > > + if (buf) > > + buf += ret; > > continue; > > } > > xbc_array_for_each_value(vnode, val) { > > @@ -456,11 +459,13 @@ int __init xbc_snprint_cmdline(char *buf, size_t > > size, struct xbc_node *root) > > xbc_namebuf, q, val, q); > > if (ret < 0) > > return ret; > > - buf += ret; > > + len += ret; > > + if (buf) > > + buf += ret; > > } > > } > > > > - return buf - (end - size); > > + return len; > > } > > #undef rest > > > > -- > > 2.53.0 > > > > > -- > Masami Hiramatsu (Google) <[email protected]> -- Masami Hiramatsu (Google) <[email protected]>
