linux-kernel - Re: [PATCH] staging: axis-fifo: fix integer overflow in write()

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Message-ID: <aOUQMZQr3JwNTUYX@stanley.mountain>
Date: Tue, 7 Oct 2025 16:05:53 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Murad Sadigov <sdgvmrd@...il.com>
Cc: Greg KH <gregkh@...uxfoundation.org>, linux-staging@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] staging: axis-fifo: fix integer overflow in write()

Hi Murad,

This can't happen because vfs_write() caps len at <= MAX_RW_COUNT.

Presumably this is your Linkedin page?
https://www.linkedin.com/in/mrdsdgv/?originalSubdomain=az

When you're doing the analysis on this sort of thing, it's nice to
have the Smatch cross function db built.  I hacked up the vfs_write()
information a bit so it says that len can't be more than 1G when
actually it's capped at 2G.  I did that so that count + len wouldn't
trigger an integer overflow warning.  Those are prevented in
rw_verify_area().

$ smdb axis_fifo_write
file | caller | function | type | parameter | key | value |
     fs/read_write.c |            vfs_write | (struct file_operations)->write |           INTERNAL | -1 |                 | long(*)(struct file*, char*, ulong, llong*)
     fs/read_write.c |            vfs_write | (struct file_operations)->write |           BIT_INFO |  0 |       f->f_mode | 0x40002,0xffffffff
     fs/read_write.c |            vfs_write | (struct file_operations)->write |          USER_DATA |  1 |             buf | 0-u64max[c]
     fs/read_write.c |            vfs_write | (struct file_operations)->write |          USER_DATA |  2 |             len | 0-1000000000
     fs/read_write.c |            vfs_write | (struct file_operations)->write |          USER_DATA |  3 |            *off | 0-1000000000
     fs/read_write.c |            vfs_write | (struct file_operations)->write |           USER_PTR |  3 |             off | 
     fs/read_write.c |            vfs_write | (struct file_operations)->write |        PARAM_VALUE |  0 |               f | 4096-9223372036854775807
     fs/read_write.c |            vfs_write | (struct file_operations)->write |        PARAM_VALUE |  0 |         f->f_op | 4096-ptr_max
     fs/read_write.c |            vfs_write | (struct file_operations)->write |        PARAM_VALUE |  0 |  f->f_op->write | 1-u64max
     fs/read_write.c |            vfs_write | (struct file_operations)->write |        PARAM_VALUE |  2 |             len | 0-1000000000,2147479552
     fs/read_write.c |            vfs_write | (struct file_operations)->write |          FUZZY_MAX |  2 |             len | 2147479552
     fs/read_write.c |            vfs_write | (struct file_operations)->write |        PARAM_VALUE |  3 |            *off | 0-1000000000
     fs/read_write.c |            vfs_write | (struct file_operations)->write |        PARAM_VALUE |  3 |             off | 0,4096-ptr_max
     fs/read_write.c |            vfs_write | (struct file_operations)->write |          CONTAINER |  0 |        -32-80+0 | $(-1)
     fs/read_write.c |            vfs_write | (struct file_operations)->write |        DATA_SOURCE |  0 |               f | $0
     fs/read_write.c |            vfs_write | (struct file_operations)->write |        DATA_SOURCE |  1 |             buf | $1
     fs/read_write.c |            vfs_write | (struct file_operations)->write |        DATA_SOURCE |  2 |             len | $2 [m]
     fs/read_write.c |            vfs_write | (struct file_operations)->write |        DATA_SOURCE |  3 |             off | $3
     fs/read_write.c |            vfs_write | (struct file_operations)->write |               2059 | -1 |                 | y
     fs/read_write.c |            vfs_write | (struct file_operations)->write |               2059 | -1 |                 | y
     fs/read_write.c |            vfs_write | (struct file_operations)->write |           BUF_SIZE |  3 |             off | (-1),8
$

regards,
dan carpenter