fs/procfs: fix potential out-of-bounds read in mount_sprintf()

[hritikkumar07]

Summary

When formatting entries for /proc/fs/mount, vsnprintf() returns the full string length even if output is truncated to fit the 64-byte info->line staging buffer. mount_sprintf() was passing this untruncated length to procfs_memcpy(), causing an out-of-bounds read past info->line when a mountpoint path was long enough (e.g. >= 50 characters).

This PR clamps linesize to info->linelen - 1 before calling procfs_memcpy(), limiting the copy to the actual bytes stored in the buffer.

Fixes #20011

Impact

• Is new feature needed? No
• Impact on user? Prevents procfs buffer overflow reads when long mount paths are present.
• Impact on build? None
• Impact on hardware? None

Testing

• Verified mount_sprintf() bounds logic when formatting long mount point paths (> 50 chars).
• Confirmed output string truncation functions properly without reading past the end of info->line.

[github-actions]

MemBrowse Memory Report

esp32-devkitc

• ROM: .flash.text +8 B (+0.0%, 124,908 B / 4,194,272 B, total: 3% used)
• irom0_0_seg: .flash.text +8 B (+0.0%, 89,112 B / 3,342,304 B, total: 3% used)

hifive1-revb

• flash: .text +12 B (+0.0%, 83,728 B / 4,194,304 B, total: 2% used)

qemu-armv8a

• Code: .text.mount_sprintf +12 B (+0.0%, 337,520 B)

qemu-intel64

• Code: .text +13 B (+0.0%, 8,659,727 B)

s698pm-dkit

• Code: .text +32 B (+0.0%, 365,200 B)
  No memory changes detected for:
• arduino-mega2560
• mirtoo
• rx65n-rsk2mb
• stm32-nucleo-f103rb

[Abhishekmishra2808]

Thank you- @hritikkumar07, before opening a PR, please take a look at https://github.com/apache/nuttx/blob/master/CONTRIBUTING.md. The check is failing due to a missing signed commit message. Please fix it

Logs:

../nuttx/tools/checkpatch.sh -c -u -m -g  907a521b15db6b1dceb4159ce1921c4f77124895..HEAD
❌ Missing Signed-off-by
Used config files:
    1: .codespellrc
Some checks failed. For contributing guidelines, see:
  https://github.com/apache/nuttx/blob/master/CONTRIBUTING.md
Error: Process completed with exit code 1.

[xiaoxiang781216]

@hritikkumar07 please fix:

cc2df0bae3 fs/procfs: fix buffer overflow in mount_sprintf
../nuttx/tools/checkpatch.sh -c -u -m -g  907a521b15db6b1dceb4159ce1921c4f77124895..HEAD
❌ Missing Signed-off-by
Used config files:
    1: .codespellrc
Some checks failed. For contributing guidelines, see:
  https://github.com/apache/nuttx/blob/master/CONTRIBUTING.md
Error: Process completed with exit code 1.

[hritikkumar07]

Hey @Abhishekmishra2808 and @xiaoxiang781216 ,
Thanks for pointing this out. I’ll fix the missing Signed-off-by in the commit message and push the updated commit shortly.