/storage/emulated/legacy is read only

For some reason, no apps on my phone (including adb, after running su) can modify any files in any subdirectory of /storage. I also can’t use my file manager on my computer to edit, create, or delete files on my phone. However, everything else works perfectly – until an app tries to save a file (all apps are still saving their databases and settings correctly – this only applies to my personal files).

Each of these files are owned by root, with group “sdcard_r”. Files have permissions -rw-rw----, and directories have drwxrwx--- which seems right. I tried reinstalling my file manager and other apps (in case their UID’s somehow left the group), and that didn’t solve anything.

My guess is the partition is mounted as read-only, but I’m not sure how to fix it, or which partitions are mounted incorrectly. This problem persists after multiple reboots.

Here’s the output of the mount command:

rootfs / rootfs ro,relatime 0 0
tmpfs /dev tmpfs rw,seclabel,nosuid,relatime,size=865064k,nr_inodes=128149,mode=755 0 0
devpts /dev/pts devpts rw,seclabel,relatime,mode=600 0 0
none /dev/cpuctl cgroup rw,relatime,cpu 0 0
proc /proc proc rw,relatime 0 0
sysfs /sys sysfs rw,seclabel,relatime 0 0
selinuxfs /sys/fs/selinux selinuxfs rw,relatime 0 0
debugfs /sys/kernel/debug debugfs rw,relatime 0 0
none /sys/fs/cgroup tmpfs rw,seclabel,relatime,size=865064k,nr_inodes=128149,mode=750,gid=1000 0 0
none /acct cgroup rw,relatime,cpuacct 0 0
tmpfs /mnt/secure tmpfs rw,seclabel,relatime,size=865064k,nr_inodes=128149,mode=700 0 0
tmpfs /mnt/asec tmpfs rw,seclabel,relatime,size=865064k,nr_inodes=128149,mode=755,gid=1000 0 0
tmpfs /mnt/obb tmpfs rw,seclabel,relatime,size=865064k,nr_inodes=128149,mode=755,gid=1000 0 0
/dev/block/platform/msm_sdcc.1/by-name/apnhlos /firmware vfat ro,context=u:object_r:firmware_file:s0,relatime,uid=1000,gid=1000,fmask=0337,dmask=0227,codepage=cp437,iocharset=iso8859-1,shortname=lower,errors=remount-ro 0 0
/dev/block/platform/msm_sdcc.1/by-name/modem /firmware-modem vfat ro,context=u:object_r:firmware_file:s0,relatime,uid=1000,gid=1000,fmask=0337,dmask=0227,codepage=cp437,iocharset=iso8859-1,shortname=lower,errors=remount-ro 0 0
/dev/block/platform/msm_sdcc.1/by-name/system /system ext4 ro,seclabel,relatime,data=ordered 0 0
/dev/block/platform/msm_sdcc.1/by-name/userdata /data ext4 rw,seclabel,nosuid,nodev,noatime,discard,journal_checksum,journal_async_commit,noauto_da_alloc,data=ordered 0 0
/dev/block/platform/msm_sdcc.1/by-name/cache /cache ext4 rw,seclabel,nosuid,nodev,noatime,discard,journal_checksum,journal_async_commit,noauto_da_alloc,errors=panic,data=ordered 0 0
/dev/block/platform/msm_sdcc.1/by-name/persist /persist ext4 rw,seclabel,nosuid,nodev,noatime,discard,journal_checksum,journal_async_commit,noauto_da_alloc,data=ordered 0 0
/dev/block/platform/msm_sdcc.1/by-name/efs /efs ext4 rw,seclabel,nosuid,nodev,noatime,discard,journal_checksum,journal_async_commit,noauto_da_alloc,data=ordered 0 0
/dev/block/platform/msm_sdcc.1/by-name/persdata /persdata/absolute ext4 rw,seclabel,nosuid,nodev,relatime,data=ordered 0 0
/dev/fuse /mnt/shell/emulated fuse rw,nosuid,nodev,relatime,user_id=1023,group_id=1023,default_permissions,allow_other 0 0
/dev/fuse /mnt/shell/knox-emulated fuse rw,nosuid,nodev,relatime,user_id=1000,group_id=1000,default_permissions,allow_other 0 0
/dev/fuse /mnt/shell/privatemode fuse rw,nosuid,nodev,relatime,user_id=1000,group_id=1000,default_permissions,allow_other 0 0
tmpfs /storage/emulated tmpfs rw,seclabel,nosuid,nodev,relatime,size=865092k,nr_inodes=128162,mode=050,gid=1028 0 0
/dev/fuse /storage/emulated/0 fuse rw,nosuid,nodev,relatime,user_id=1023,group_id=1023,default_permissions,allow_other 0 0
/dev/fuse /storage/emulated/0/Android/obb fuse rw,nosuid,nodev,relatime,user_id=1023,group_id=1023,default_permissions,allow_other 0 0
/dev/fuse /storage/emulated/legacy fuse rw,nosuid,nodev,relatime,user_id=1023,group_id=1023,default_permissions,allow_other 0 0
/dev/fuse /storage/emulated/legacy/Android/obb fuse rw,nosuid,nodev,relatime,user_id=1023,group_id=1023,default_permissions,allow_other 0 0

I have a rooted T-Mobile Galaxy S5 running stock Android 5.0. The issue started after I accidentally launched recovery mode, but I didn’t do anything – actually, I assumed that it was unrelated at first. Does anyone know how to resolve this?