w1: ds2482: Fix signedness bug in ds2482_w1_triplet()

ds2482_wait_1wire_idle() returns the status register value (0..255) on
success, or a negative value on I2C failure: -1 when selecting the
status register fails, or a negative errno from i2c_smbus_read_byte().

ds2482_w1_triplet() feeds that result into "return (status >> 5);"
without checking for errors, and the function returns u8. For a
negative status the arithmetic shift keeps the sign and the u8
truncation fabricates a triplet result whose meaning depends on the
errno value: -1 and -EIO happen to become 0xff, whose set low bits make
w1_search() abort, but -ETIMEDOUT (-110 >> 5 = -4) becomes 0xfc -
"devices responded on both branches, wrote 1" - and -EOPNOTSUPP
(-95 >> 5 = -3) becomes 0xfd - "only the zero branch responded".
w1_search() then continues the ROM search with a fabricated direction
bit instead of aborting, and the corrupted id is either rejected by the
ROM CRC (existing device missed) or registers a phantom slave.

The function already defines an in-band error value: status is
initialized to (3 << 5), which decodes to 3 (both branch bits set, "no
device responded") and makes w1_search() terminate the search when
sending the triplet command fails. Decode a negative status to the same
value.

Found by smatch:
drivers/w1/masters/ds2482.c:314 ds2482_w1_triplet() warn: signedness bug returning '(-67108864)'

Fixes: baf12ae29ab4 ("[PATCH] W1: Add the DS2482 I2C-to-w1 bridge driver.")
Assisted-by: Claude:claude-sonnet-5
Signed-off-by: Babanpreet Singh <bbnpreetsingh@gmail.com>
Link: https://patch.msgid.link/20260714041011.7-1-bbnpreetsingh@gmail.com
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>

0 files changed, 0 insertions, 0 deletions