The patch titled Subject: lib/buildid: use __kernel_read() for sleepable context has been added to the -mm mm-hotfixes-unstable branch. Its filename is lib-buildid-use-__kernel_read-for-sleepable-context.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Shakeel Butt shakeel.butt@linux.dev Subject: lib/buildid: use __kernel_read() for sleepable context Date: Mon, 22 Dec 2025 12:58:59 -0800

Prevent a "BUG: unable to handle kernel NULL pointer dereference in filemap_read_folio".

For the sleepable context, convert freader to use __kernel_read() instead of direct page cache access via read_cache_folio(). This simplifies the faultable code path by using the standard kernel file reading interface which handles all the complexity of reading file data.

At the moment we are not changing the code for non-sleepable context which uses filemap_get_folio() and only succeeds if the target folios are already in memory and up-to-date. The reason is to keep the patch simple and easier to backport to stable kernels.

Syzbot repro does not crash the kernel anymore and the selftests run successfully.

In the follow up we will make __kernel_read() with IOCB_NOWAIT work for non-sleepable contexts. In addition, I would like to replace the secretmem check with a more generic approach and will add fstest for the buildid code.

Link: https://lkml.kernel.org/r/20251222205859.3968077-1-shakeel.butt@linux.dev Fixes: ad41251c290d ("lib/buildid: implement sleepable build_id_parse() API") Reported-by: syzbot+09b7d050e4806540153d@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=09b7d050e4806540153d Signed-off-by: Shakeel Butt shakeel.butt@linux.dev Reviewed-by: Christoph Hellwig hch@lst.de Cc: Alexei Starovoitov ast@kernel.org Cc: Andrii Nakryiko andrii@kernel.org Cc: Daniel Borkman daniel@iogearbox.net Cc: "Darrick J. Wong" djwong@kernel.org Cc: Matthew Wilcox (Oracle) willy@infradead.org Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

lib/buildid.c | 32 ++++++++++++++++++++------------ 1 file changed, 20 insertions(+), 12 deletions(-)

--- a/lib/buildid.c~lib-buildid-use-__kernel_read-for-sleepable-context +++ a/lib/buildid.c @@ -5,6 +5,7 @@ #include <linux/elf.h> #include <linux/kernel.h> #include <linux/pagemap.h> +#include <linux/fs.h> #include <linux/secretmem.h>

#define BUILD_ID 3 @@ -46,20 +47,9 @@ static int freader_get_folio(struct frea

freader_put_folio(r);

- /* reject secretmem folios created with memfd_secret() */ - if (secretmem_mapping(r->file->f_mapping)) - return -EFAULT; - + /* only use page cache lookup - fail if not already cached */ r->folio = filemap_get_folio(r->file->f_mapping, file_off >> PAGE_SHIFT);

- /* if sleeping is allowed, wait for the page, if necessary */ - if (r->may_fault && (IS_ERR(r->folio) || !folio_test_uptodate(r->folio))) { - filemap_invalidate_lock_shared(r->file->f_mapping); - r->folio = read_cache_folio(r->file->f_mapping, file_off >> PAGE_SHIFT, - NULL, r->file); - filemap_invalidate_unlock_shared(r->file->f_mapping); - } - if (IS_ERR(r->folio) || !folio_test_uptodate(r->folio)) { if (!IS_ERR(r->folio)) folio_put(r->folio); @@ -97,6 +87,24 @@ const void *freader_fetch(struct freader return r->data + file_off; }

+ /* reject secretmem folios created with memfd_secret() */ + if (secretmem_mapping(r->file->f_mapping)) { + r->err = -EFAULT; + return NULL; + } + + /* use __kernel_read() for sleepable context */ + if (r->may_fault) { + ssize_t ret; + + ret = __kernel_read(r->file, r->buf, sz, &file_off); + if (ret != sz) { + r->err = (ret < 0) ? ret : -EIO; + return NULL; + } + return r->buf; + } + /* fetch or reuse folio for given file offset */ r->err = freader_get_folio(r, file_off); if (r->err) _

Patches currently in -mm which might be from shakeel.butt@linux.dev are

mm-memcg-fix-unit-conversion-for-k-macro-in-oom-log.patch lib-buildid-use-__kernel_read-for-sleepable-context.patch