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Mon, 1 Sep 2025 03:30:40 -0400 (EDT) From: Janne Grunau Date: Mon, 01 Sep 2025 09:29:43 +0200 Subject: [PATCH] nvmem: core: Fix OOB read for bit offsets of more than one byte Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20250901-nvmem-read-oob-bit-offset-v1-1-b610e18cdd3c@jannau.net> X-B4-Tracking: v=1; b=H4sIAGZLtWgC/x3MPQqAMAxA4atIZgNtRUGvIg79STSDrbQignh3i +M3vPdAoSxUYGoeyHRJkRQrdNuA32xcCSVUg1GmV6PSGK+ddsxkA6bk0MmJibnQicFrb7gbLQ8 ean9kYrn/97y87wdTMWahawAAAA== X-Change-ID: 20250901-nvmem-read-oob-bit-offset-dc1c2f39af6c To: Srinivas Kandagatla , Dmitry Baryshkov , Greg Kroah-Hartman Cc: linux-kernel@vger.kernel.org, Janne Grunau X-Mailer: b4 0.14.2 X-Developer-Signature: v=1; a=openpgp-sha256; l=1625; i=j@jannau.net; s=yk2024; h=from:subject:message-id; bh=fCl1OJWst0doBUXz5EoM/vsthT5itOxtexrKclhgl0I=; b=owGbwMvMwCW2UNrmdq9+ahrjabUkhoyt3vNb3TqP3vRRWaEmdWgZ78NlgmXBYaKdvWrzd9SfZ +sPPCbQUcrCIMbFICumyJKk/bKDYXWNYkztgzCYOaxMIEMYuDgFYCJ62YwM8/5ryaW0qq70KGLL Kk59o7hulX2bTe2xV4Fnzk/T2jxvKcP/yHs7n7sHcBSeXf/17dFPtiet+TX4Qrkl7j1TW3pFSzK bAQA= X-Developer-Key: i=j@jannau.net; a=openpgp; fpr=8B336A6BE4E5695E89B8532B81E806F586338419 When the bit offset is BITS_PER_BYTE or larger the read position is advanced by `bytes_offset`. This is not taken into account in the per-byte read loop which still reads `cell->bytes` resulting in an out of bounds read of `bytes_offset` bytes. The information read OOB does not leak directly as the erroneously read bits are cleared. Detected by KASAN while looking for a use-after-free in simplefb.c. Fixes: 7a06ef7510779 ("nvmem: core: fix bit offsets of more than one byte") Signed-off-by: Janne Grunau --- drivers/nvmem/core.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c index 387c88c55259541446901f0e539bbb0dd8c4c3de..19be16943ee66e845860192b8f0= 08539873f6f7f 100644 --- a/drivers/nvmem/core.c +++ b/drivers/nvmem/core.c @@ -1618,12 +1618,14 @@ static void nvmem_shift_read_buffer_in_place(struct= nvmem_cell_entry *cell, void *p =3D *b++ >> bit_offset; =20 /* setup rest of the bytes if any */ - for (i =3D 1; i < cell->bytes; i++) { + for (i =3D 1; i < (cell->bytes - bytes_offset); i++) { /* Get bits from next byte and shift them towards msb */ *p++ |=3D *b << (BITS_PER_BYTE - bit_offset); =20 *p =3D *b++ >> bit_offset; } + /* point to end of the buffer unused bits will be cleared */ + p =3D buf + cell->bytes - 1; } else if (p !=3D b) { memmove(p, b, cell->bytes - bytes_offset); p +=3D cell->bytes - 1; --- base-commit: 8f5ae30d69d7543eee0d70083daf4de8fe15d585 change-id: 20250901-nvmem-read-oob-bit-offset-dc1c2f39af6c Best regards, --=20 Janne Grunau